_
[Previous]
[Contents]
[Next]
[Comments or questions]
[Marketing Needed -- Can You Help?]
Copyright © 1996-2005 jsd
12 Landing
-
-
-
Pilots spend a lot of time doing “traffic pattern work” ---
a series of touch-and-goes. Non-pilots imagine this as being
analogous to driving into a parallel-parking space, then
immediately pulling out, driving around the block, and
repeating the process --- over and over again.
Landings involve procedures and perceptions that are just a little bit
different from those involved in other phases of flight. A few of
them are discussed in this chapter. (Special procedures for forced
landings are discussed in section 15.1.)
12.1 Planning the Approach
The approach checklist should cover three things: approach,
landing, and go-around. At the point where you decide to
perform a go-around, you will be in no mood to go looking for a
checklist.
By the same logic, by the time you are established on downwind in
preparation for landing, it is already too late to be reading the
approach checklist. Therefore, the practical way to use the approach
checklist is to review it before entering the traffic
pattern. A few miles from the airport, read the checklist, think
about it, and commit it to memory. Say it aloud several times if you
like.1 Short-term memory is considerably more reliable than
long-term memory. Remember that the checklist is not a “do-list”;
you don’t have to do each item at the moment you read it on the
checklist.
You probably want to make a pocket checklist, as discussed in
section 21.6. Make sure you use a written checklist that
applies to the airplane you are actually flying. That is, don’t
bother trying to memorize some “universal” checklist. Different
airplanes have different checklists.
12.1.1 Other Planning Issues
In flight, you know you have to
land sooner or later, but you should never allow yourself to get into
a situation where you think you have to land on this runway
right now. If you are approaching a soft, narrow, short runway
with gusty crosswinds and the setting sun in your eyes, it might be a
lot safer to land somewhere else. You might
have to get a ride from the second airport back to the first, or you
might just wait on the ground until conditions improve.
On approach and in the traffic pattern, be extra-careful to see and
avoid other traffic. This is discussed in section 16.2.
12.1.3 Obstacle Clearance
A particularly risky combination is night VFR
at an unfamiliar field. I recommend you don’t attempt this, unless
you remove at least one of the risk factors.-
If you are planning night VFR, stick to fields that you have
visited in the daytime often enough to know the tricks for
avoiding the local obstacles, if any.
- If you are going to an
unfamiliar field at night, follow the IFR procedures. Don’t try to
invent your own procedure, because non-IFR sources such as the A/FD
and sectional charts simply do not give you enough information to do
this safely.
- If you are going to an unfamiliar field VFR, go in the daytime,
in good weather, so you can see the terrain and obstructions.
See section 13.7.5 and section 21.4 for
more discussion of these points. Don’t get complacent. You may know
of dozens or hundreds of airports where obstacles are easy to avoid
... but sooner or later you will visit an airport where obstacles are
a real threat, and you don’t want to run even a small-percentage
chance of finding this out the hard way.
If the approach procedure says “no circling southeast of the field”
you should take the hint.
Don’t descend below a safe circling altitude until you have a nice
view of the green threshold lights. They should not be blinking
or twinkling, as discussed in section 12.3.
12.2 Judging Left or Right
Let’s consider how things are supposed to look on final approach. One
important ingredient is to be correctly lined up left/right. The task
of getting lined up with a far-away object, without any intermediate
guideposts, is unfamiliar to most people.
Figure 12.1, figure 12.2, and
figure 12.3 show how the runway looks if you are lined
up too far to the left, perfectly on the runway centerline, or
too far to the right (respectively).
The distinctions are easy enough to perceive, once
you learn how. In all cases, one of the key ideas is to notice
that point A lies directly above point B. That means you are
lined up on the line from B to A. In particular, we see that
in figure 12.1 and figure 12.3, you are exactly
half a runway-width to one side. That is, you are lined up on
one of the runway edge lines. If you continue with such an approach,
you will mow down all the runway edge lights.
If while on final you perceive that you are lined
up left or right of the extended centerline, you should not
just fly directly toward the point of intended landing. Instead,
you should fly over to the extended centerline now and
then follow it to the runway. The objective is to be traveling
in the right direction when you arrive at the runway.
As discussed in section 12.6.2 and section 12.11.1,
you will not be able to see the runway centerline during critical
parts of the flare, touchdown, and initial rollout. You need
to maneuver to reference to the runway edge. You should
start applying this skill on short final. If the runway is 40
feet wide, you should say to yourself “I’m lined up 20 feet
this side of the edge line.... I’m lined up 20 feet this side
of the edge line...”.
Land on the center line
by reference to the edge line.
|
|
Don’t fixate on the centerline --- it will disappear
during the flare.
12.3 Judging High or Low; Rule of Thumb
Even more important than having the left-or-right alignment is having
the proper up-or-down alignment of the approach path. There are
several ways to do this.
One of the worst ways is to use “local tricks”, such as passing over the pond at 1500 MSL and then
passing over the old red barn at 1000 MSL. Such an approach procedure
doesn’t work too well when you visit other airports.
The smart way
to control the slope of the glide is to observe and control the slope
angle directly. On an instrument approach, the electronic
glideslope needle defines a 3 degree angle
for you. At some airports there is a visual aid such as a VASI to
define the angle for you. At most airports, though, there is no such
guidance, so you simply must learn to perceive angles accurately.
Most people are terrible at judging angles using
the unaided eye. Therefore I recommend the following rule of
thumb:
|
A thumb at arm’s length subtends four degrees.
|
|
Specifically, the rule of thumb refers to the distance between
the last joint and the end of the thumb, as shown in figure 12.4.
Figure 12.4: Rule of Thumb --- 4 Degree Glideslope Angle
To use this rule, hold your thumb at arm’s length, and arrange
it so your sight line over the end of the thumb extends to the
forward horizon, as shown in the figure. Then the sight line
over the last joint of the thumb will be four degrees below the
horizon. If this sight line extends to your chosen aim point,
you know you are on a nice 4 degree glideslope.
In order to make clear the geometry of the situation, figure 12.4 shows how your eye, your thumb, etc. will appear as
viewed by your copilot. Figure 12.5 shows how it
looks from your own point of view.
Note that for reasons discussed in section 12.7.3, the
aim point is generally not the runway threshold.
Your thumb may not be exactly the same size as mine, but if your
thumb is smaller your arm is probably shorter and the angle is
probably close to four degrees. In any case, you should learn
what angle is subtended by your own thumb2
--- it comes in really handy.
Another application of this “rule of thumb” is to help
perceive the destination of a power-off glide, as described in
section 15.1.4.
The next question is, how do you know you are actually following
the 4 degree glideslope, as opposed to merely passing through it?
Answer: as long as you remain on that glideslope, the aim point will
remain four degrees below the horizon.
This is the correct strategy: throughout the final approach segment,
your chosen aim point should remain below the horizon by the desired
number of degrees.3 To say it the
other way, if the angle between the horizon and your aim point is
changing, then your intended destination is not your
actual destination.
If the angle from the horizon to the aim point is increasing, you are
going to land long; if the angle is decreasing, you are going to land
short --- unless you somehow change what you’re doing. The logic of this
is shown in figure 12.6.
The airplane in the figure is flying directly toward point X. It
will overfly point A but land short of point Z. As the airplane
moves from position 1 to position 2, the angle of A below the
horizon increases to 90 degrees and beyond. The angle to point X
remains constant, while point Z appears to move closer to the
horizon.
If you are on final and perceive the aim point shrinking
up toward the horizon, you probably need to add power. Conversely,
if you see the angle growing (3
degrees... 3.5 degrees... 4 degrees...),
you probably need to reduce power and/or increase drag.
Given that the angle shouldn’t change, what sort of angle is suitable?
Within the reasonable range (three to six degrees) it usually isn’t
critical which angle you choose. Here are the main considerations:
If you make a too-steep approach,
it makes the flare maneuver more difficult and more critical. Also, some
aircraft have so little drag (even in the landing configuration)
that they have a hard time staying on a steep glideslope, unless
they get help from a headwind.
Conversely, if you fly a too-shallow approach,
you need to worry about running into obstructions. It also
leaves you with fewer options in the event of an engine failure on
final.
Generally, if the angle from the horizon to the aim point is less than
three-quarters of a thumb (less than three degrees),
you are flying a too-shallow approach. Conversely, if the angle is
more than a thumb and a half (more than 6 degrees), you are flying an
abnormally steep approach.
In all cases you should be extremely sensitive to changes
in the angle, since that tells you whether
you are going to land long or land short.
12.4 Judging Pitch Attitude and Angle of Attack
Now we come to
the most critical task of all: you must control the angle of attack.
This is important in all phases of flight, but especially so
on final approach when you are intentionally rather low and slow.
12.4.1 Use Outside References and Trim
One way to maintain a definite angle of attack is to carefully
perceive and control both the pitch angle and glideslope angle, as
shown in figure 12.7.
As discussed in chapter 2, for any given flap
setting the angle of attack depends on the difference between
the pitch attitude and the direction of flight. Therefore if
you maintain a definite value for those two angles, you are also
maintaining a definite value for the angle of attack.
Trimming the airplane for the desired angle of attack
and flying with a light touch on the controls is also exceedingly
helpful in maintaining a definite value for angle of attack; see
section 12.12.
To make sure the value in question is the correct value, you
should look at the airspeed: indicator every so often, but that
should constitute only 10% of your looking. The other nine looks out
of ten should be directed toward the outside, such as the angles in
figure 12.7.
Controlling angle of attack is even more important
than controlling the left-or-right and up-or-down alignment of
the flight path. If you show up at the runway slightly misaligned,
or slightly long, it is usually not tragic and it is usually obvious
how to solve the problem (perhaps by going around). On the other
hand, if you lose control of the angle of attack, your flying
career could end quite suddenly.
12.4.2 Observe and Control More Than One Thing
For any given flap setting, there are three vertical angles of
interest:
-
the glideslope angle,
i.e. the
angle of the aim point below the horizon,
- the pitch attitude,
i.e. the angle of the nose below the horizon, and
- the angle of attack, which depends on the angle of
the nose relative to the aim point.
As discussed below, if you perceive and control
any two of these angles, you automatically control the third.
Some pilots (especially students) try to oversimplify the situation by
worrying about only one of the three angles. This leaves the
other two angles completely uncontrolled. Figure 12.8
shows three examples of what can happen if you control only one angle,
namely the aim point relative to nose:
-
The lowest airplane has the aim point in the
right place on the windscreen. However another angle, namely
the glide slope angle, is wrong, so you hit the obstruction.
- The middle airplane is just right. All three
angles have their correct values. You got lucky.
- The highest airplane once again starts out with
the aim point just the right angle above the nose, but this does
not mean that the angle of attack is correct, because the
airplane is not actually moving toward the aim point. Another angle,
namely the angle between the aim point and the horizon, is too big and
(what’s worse) it’s changing. To keep the aim point the “right”
angle above the nose, you foolishly keep pushing harder and harder on
the yoke. At every point along this curved path you’ve got too much
energy, but you don’t know
it because you are only watching one angle.
For a typical person in a typical airplane, on final approach you can
easily see the aim point over the nose. If one day the nose of the
airplane comes up and blocks your view of the aim point, you should
notice immediately and be at least somewhat alarmed.
There are several possibilities. The most alarming ones are:
-
Possibly your pitch attitude is too high (meaning
you might be about to stall).
- Possibly you are not really moving toward your
chosen aim point (meaning you are about to land long).
- Possibly you have both problems (long and slow).
Less-disastrous possibilities include the following:
-
If you
ever find yourself on approach with too much airspeed and too
little altitude, it is OK to raise the nose and zoom back up to
the correct glideslope. During this correction maneuver, the
nose will (temporarily!) block your view of the aim point. Still,
it remains a topic of concern: if the nose comes up like this,
you should have a special reason, and it must be very temporary.
- If you switch to an airplane with a longer, wider, and higher
snout, it might block your view during a normal approach.
- If you have a short torso, you might have trouble seeing the
aim point even if your copilot can see it easily.4
- If you use less than full flaps, it will
make the problem worse.
- An unusually large headwind will make the problem worse.
Note that the converse does not hold; maintaining a proper view of the
aim point does not solve all the world’s problems, as was illustrated
by figure 12.8. To control the airplane properly,
you absolutely must perceive and control more than one angle.
In theory, you could concentrate on any two of these angles and let the
third one take care of itself. On the other hand, it’s not really any
extra work to keep track of all three, and each one is
interesting for its own special reason:
-
I watch very closely the angle between the horizon
and the aim point, because this one is related to energy. Since
energy problems cannot be solved quickly, it really pays to notice
small changes in this angle as early as possible.
- As my second angle, I watch the nose relative
to the horizon. This is a strong habit. I always watch
the nose relative to the horizon, whether I am climbing, descending,
or flying level.
- The third angle (the position
of the aim point on the windshield) is particularly interesting
because it is related to angle of attack. It has the nice property of
remaining more-or-less5 constant from one approach to the next, whereas the
other two angles will change quite a bit depending on whether it is
a steep approach or a shallow approach. Committing this angle
to memory makes it possible to land without using the airspeed
indicator.
Additional discussion of too-steep or too-shallow
approaches can be found in section 12.3.
12.4.3 Correct for Wind
There is one more ingredient in this recipe: the
wind. As we shall see, in the presence of wind your direction
of flight relative to the ground is not the same as your direction
of flight through the air. You need to be able to perceive both.
Suppose you are on a nice 3 degree glideslope, doing
90 knots in no-wind conditions. Your direction of flight is 3
degrees below the horizon and the relative wind is therefore originating
3 degrees below the horizon. Now suppose a headwind of 30 knots
springs up. You add power to remain on the 3 degree glideslope.
Your flight path relative to the ground is still three degrees
below the horizon, but the flight path through the windy air is
only two degrees below the horizon.
Figure 12.9 may clarify the situation.
The approach commences from a point 1 mile from the runway and
300 feet up; this constitutes a 3 degree glideslope. In the absence
of wind, the approach is flown as shown in figure 12.10.
You have 90 knots of true airspeed (90 KTAS) and 450 fpm of descent
rate. You will reach the runway in 40 seconds.
As shown in figure 12.11, in the presence
of wind you have only 60 knots of groundspeed --- two thirds as
much as in the no-wind case. In order to stay on the 3 degree
glideslope, you must descend at two thirds of the rate. This
is why you had to add power.
At the reduced groundspeed, it will take you an entire
minute to reach the runway. At the end of that minute, the small
hot-air balloon that is in the middle of the runway in
figure 12.12 will have been blown a half mile, and will meet
you right at the runway threshold. Therefore your path through
the air is not aimed toward the threshold, but is aimed toward
the balloon. Your direction of flight through the air is only
two degrees (not three degrees) below the horizon.
The relative wind is the reciprocal of the direction
of flight through the air. The wing
doesn’t care about your groundspeed; it only cares about the angle
of attack, which depends on the relative wind. To maintain the
proper angle of attack the pitch attitude will be one degree higher
than in the no-wind case.
Conclusion: First, you need to perceive your direction of flight
relative to the ground, so you can be sure you will arrive at the aim
point as intended. Second, you need to perceive your direction of
flight through the air, so you can know what pitch attitude is
required to give the desired angle of attack. If you are descending
into a headwind, you will need less rate of descent; in any situation
where you have less descent you will need less nose-down attitude.
Note that the scheme of estimating the relative wind
using the ratio of vertical speed to airspeed gives the correct
answer even when nature’s wind is blowing. As shown in figure 12.13, you have a normal airspeed and a reduced
VSI indication while plodding down the
glideslope into the wind. See section 2.11, including
figure 2.12, for some discussion of how this
looks on the instruments.
Figure 12.13: Vertical, Horizontal Speeds Determine Angle
(Side View)
12.5 Other Perceptions
Instruments: About one look out of ten, you should look at the
airspeed: indicator on final
approach. The other nine looks out of ten, you should look outside,
judging the angles as described above. During the flare, you should
definitely be looking outside, not at the gauges. You want to land the
airplane at a very high angle of attack. You will have to perceive the angle of attack using outside
visual cues. During the flare, the
airspeed indicator doesn’t tell you anything about angle of attack (as
discussed in section 2.12) or anything else you need to know.
I once asked an experienced airline captain to tell me at what
airspeed his airliner touched down. He said “I don’t know; I never
looked. I always have more important things to look at”. That was
a good pilot’s honest answer.
Wind drift: On the base leg, you should make it a habit to check your
wind drift. Normally you are being blown away from the airport,
meaning that after you turn onto final you will have a headwind. If
you are being blown toward the airport, watch out!
Groundspeed: Obviously you should choose a runway that is headed into
the wind, so you can land with a low groundspeed. However, beyond the
choice of runway, you have little control over groundspeed. Your
primary duty is to control airspeed, so you are pretty much stuck with
whatever groundspeed results.
Also, it is hard to perceive groundspeed accurately.
The perceptions will change according to
-
the amount of headwind
- day versus night landing
- the model of airplane
- density altitude
See section 12.7.4 for a long list of perceptions you can
use to make sure you are landing into the wind at the right speed.
12.6 Basic “Normal” Landing
Your Pilot’s Operating Handbook should specify a “normal” landing
procedure. It would probably be more accurate to rename it the
“basic” landing procedure, for a simple reason: Many pilots are
based at short, unpaved, or crosswindy airports. For them, the basic
procedure is definitely not their “normal” procedure. The basic
procedure should be thought of as the basis, the foundation on which
other techniques are built.
In any case, here are the elements of the basic landing
procedure: (1) the final approach, (2) the flare, and (3) the
rollout.
The main aspects of the final approach were discussed
in previous sections.
The term flare refers to the part of the flight
where you are raising the nose, from the nose-down attitude on
final approach to the nose-high attitude at touchdown.
Throughout the flare process, raise the nose smoothly.
It is a common mistake to raise the nose stepwise, that is, to
raise the nose a little bit, see what happens, and then raise
it a little bit more, and so forth. You should not ask yourself
“How much should I raise the nose?” It is much better
to ask yourself “At what rate should I be raising the nose?”
At each point in this process, you need to worry
about three timescales: how long is it until ...
-
... your flight path becomes horizontal
- ... you reach the proper airspeed for touchdown
- ... you reach ground level
Those are the three main dependent variables that
are the result of the maneuver.
Correspondingly, the three key
independent variables that you use to control the maneuver are
-
... the airspeed you have before starting the flare
- ... the height at which you begin the flare
- ... the rate at which you raise the nose
Typically you make the decisions in
that order: First you pick an airspeed. That determines the height at
which you must flare (the faster the speed the higher the flare).
Then you adjust the rate accordingly.
In ideal conditions, you can schedule it so that
all three things happen at the same time. For any given airspeed,
if you start your flare at the right height and raise the nose
at the right rate, you can arrange that by the time you reach
ground level, you are just beginning to fly horizontally, and
your attitude is just right for touchdown.
If the
altitude, direction of flight, and attitude are just right, they
imply that your angle of attack, airspeed, and energy are just
right, too.
In less-than-ideal conditions, you should not attempt
this ideal three-way timing. This is because in the real world
you need to worry about wind gusts. You don’t want a wind gust
to come along and rob you of your airspeed while you are still
several feet above the ground, in the round part of your roundout.
Therefore, in real-world conditions you should arrange that items (a)
and (b) happen at the same time, and item (c) happens later, as shown
in figure 12.14. That is, the flare really has two
parts:
-
During the first part, called the
roundout, you are making the transition
from steadily descending flight to horizontal flight.
- During the second part, called skimming, you are
moving along horizontally, a foot or less above the ground, waiting
for the airspeed to bleed off so you can touch down at the proper
airspeed.
Continue skimming, gradually raising the nose, until the angle of
attack has increased to the point where you can land on the
main
wheels, with the nose wheel definitely in the air.6 To say it the other way, a flat, “three-point”
landing, with all three wheels making
contact at the same time, is proof that your angle of attack is much
too low and your airspeed is much too high.
If you find that the skimming phase lasts longer
than necessary, then you started with too much airspeed and/or
you began the flare too late. If you had too much airspeed on
final, next time get rid of it earlier.
Every so often I get a student who thinks it is a good idea to wait
until the last possible moment and then raise the nose all at once. I
call this a “square flare”. Even though you can get away with this
under some circumstances, it is a bad idea for the following reasons:
- There is no margin for error. If you misjudge,
and wait a little too long to perform the square flare, you will
make an airplane-shaped hole in the runway.
- It puts the instructor in an unpleasant situation. If you
don’t start the flare at the proper time, I can’t just sit there,
hoping you will do the square flare at the last moment. I have to
take control of the airplane, which will hurt your feelings if you
think it wasn’t necessary.
- The square flare doesn’t work in all circumstances.
Yes, you can get away with it in certain light trainers when
your airspeed is much faster than your stalling speed, but in
an airplane with a higher stall speed, the wing can’t develop
enough lift to force such a sudden change in direction of flight.
- You can’t reliably know how much to pull back.
If you move to a different brand of plane, or if your plane isunusually lightly loaded, or if you fly the approach at an unusual
airspeed, the square flare will go awry and you’ll have no time
to compensate.
There is no point in learning the square-flare technique
(which will work in just a few airplanes, some of the time), when
with the same amount of effort you can learn a technique that
works in all sorts of airplanes, and gives a much greater margin of
safety.
Remember, good pilots are judged on their smoothness, not their
quickness.
In the proper touchdown attitude (in most airplanes),
the nose will block your forward view. You will not be able to
see the runway centerline. Therefore, during the latter part
of the flare, during the touchdown, and during the initial parts
of the rollout, you will have to guide the plane by reference
to the runway edge. Otherwise, one of two things will
happen: (1) If you manage to keep the centerline in view, you
will touch down with much too low a pitch attitude and much too
high a speed. (2) If you raise the nose anywhere near enough,
you will lose sight of your reference and become an unguided missile.
If the stall warning horn comes on
during the skimming phase, when you are flying horizontally a few
inches above the runway, it is a good sign. You will be touching down
shortly.
Conversely, if the stall warning horn comes on early
in the roundout, when you are still several feet above the runway
and descending, it is a bad sign. You should add power immediately.
Adding power helps in two ways: (1) The power-on stalling speed
is lower than the power-off stalling speed (because of the propwash
over the wings). This might give you enough lift to arrest the
descent. (2) The added power contributes to the energy budget,
so you can rebuild your airspeed.
12.6.3 Timing the Flare
How do you recognize when it is time to begin the flare?
Let us begin by mentioning a few unhelpful answers to this question.
-
You could wait until you see the hair on the instructor’s neck
stand on end, then begin the flare. This is not good preparation
for flying solo.
- Many books suggest beginning the flare at about the height of a
typical hangar. This doesn’t work very well if you visit some place
that has bigger hangars, smaller hangars, or no hangars at all. It
also isn’t very reliable at night.
- Some people like to flare at about half the height of a typical
tree. Alas, trees work even worse than hangars, for similar reasons.
- You could wait until the width of the runway subtends a certain
angle in your field of vision. This will get you into trouble if you
visit some place with a wider or narrower runway.
- You might think of using the perception of the ground rushing
past, which does depend on height. Alas, this is hard to perceive,
and is unacceptably sensitive to the amount of headwind.
- You could try to use the depth perception that comes from
having two eyes. However, human binocular stereopsis is absolutely
useless at distances of 20 feet or greater. By the time this depth
perception comes into play, it’s too late. Wiley Post was blind in
one eye, but that didn’t prevent him from making good landings.
Here is something that actually helps: Use your sense of
timing. At each moment on short final, ask yourself how much
time t remains until you would, at the current rate, reach zero
AGL. When this time t reaches the special value tF (about two
seconds), start your flare. (The exact value of tF
will depend on what sort of airplane you’re flying, and other
factors.)
Of course the actual flare will take longer than tF --- roughly
twice as long. That’s because tF refers to what would
happen if you forgot to flare. During the actual flare, your descent
rate is reduced, so you take longer to descend.
This timing technique has some nice properties. It works on wide and
narrow runways both. It works during daytime and nighttime both. It
causes you to flare at a greater-than-usual height if you have a
greater-than-usual vertical speed.
Now all you need is some way to perceive how much time t remains.
You don’t need to know the height in feet or the descent rate in feet
per second; all you need is some quantity that perceptibly
changes as you approach zero AGL. Figure 12.15 shows one
such quantity. The left side of the figure is what you should see
when you are on final, at a definitely nonzero height. The letters
ABCD and WXYZ represent landmarks along the side of the runway.
In particular, for night landings you would use the runway lights as
landmarks.
The important thing to notice is that the landmarks are not all
colinear. In particular, BDZ is a triangle that covers nonzero area
in your field of view.
Now, in contrast, imagine that you are on your hands and knees on the
runway, so that your eye is just at the same height as the runway
lights, about 12 inches AGL. Suppose that landmarks A and W are
behind you, but you can still see the others. As shown in the right
side of the figure, all the landmarks have become colinear. The
erstwhile triangle BDZ has flattened out and now has zero area.
Of course you never actually fly with your eyes at zero AGL.
Therefore you need to observe the rate at which triangle BDZ
is gradually flattening out. By combining this rate perception with
a sense of timing, you can decide when to begin the flare.
You can practice this perception indoors: Put a book on a table, then
lower your head until the corners of the book-cover all line up.
12.6.4 Touchdown and Rollout
Don’t land with the brakes applied. Of course your
feet must be on the rudder pedals; just make sure you aren’t accidentally
depressing the brake pedals even a little bit. Wait until there
is plenty of weight on the wheels (i.e., after the nosewheel is
on the ground) before applying the brakes.
At touchdown and thereafter, the airplane should
be sufficiently well centered that the centerline is between the
main wheels. On a narrow runway you have no choice, but on a
wide runway you should land on the centerline anyway. See how
close you can come. Make it a matter of self-discipline and pride.
The touchdown should be gentle enough that the nosewheel stays in the air during touchdown and during
the first 50 feet of the rollout. This is a good way of proving to
yourself (and to all the kibitzers in the airport lounge) that you
were in complete control of the landing. To say it the other way, if
you hit with a lot of vertical momentum, it will force the nosewheel
down like a mouse trap. See also section 12.11.7.
Stay in control during the rollout. Remember, the
flight isn’t over until the aircraft is tied down. The
NTSB files
are full of reports of pilots who made a decent touchdown and
then (a quarter mile later) stopped paying attention and had an
accident.
After you have taxied clear of the runway, perform the after-landing
checklist. This will include items
such as carburetor heat off, flaps retract, cowl flaps
open, strobes off (for night taxiing, so you don’t blind everybody),
boost pumps off, et cetera.
12.7 High-Performance Landing
This section discusses the tradeoffs you must make
when the field is short, obstructed, and/or plagued by gusty winds.
The key elements of a high-performance landing are:
-
choose the right runway,
- use the right configuration,
- touch down at the right point,
- touch down at an appropriately low airspeed, and
- use the brakes effectively.
12.7.1 Choose the Right Runway
Consult your Pilot’s Operating Handbook to see how much runway you
will need, as a function of headwind, density, and other variables.
Make sure your chosen runway is long enough. Include a safety margin,
because the numbers in the book are based on perfect pilot technique,
and you don’t want to put yourself in a situation where perfection is
required. Also, for reasons discussed in section 12.7.4,
even if you have a headwind, make sure you could safely land on the
chosen runway without a headwind. And avoid landing with a
tailwind!
While you’re at it, plan ahead. Do your short-field takeoff
planning before landing at an unfamiliar short field, since in many
airplanes it is quite possible to get into a field that you can’t get
out of. Usually any runway that is good enough for takeoff is more
than good enough for landing, for reasons discussed in
section 13.7.2.
12.7.2 Use the Right Configuration
As discussed in section 5.5, extending the flaps has
six main effects:
-
Flaps decrease the stalling speed.
- Flaps increase drag.
- Flaps increase the incidence.
- Flaps increase the washout.
- Flaps perturb the trim speed.
- Flaps lower the permissible top speed.
These influence the landing in various ways:
-
1)
- Having a low stalling speed is always good.
- 2a)
- The typical short field is not just short, it’s
obstructed. Because of the obstructions, you want to make a relatively
steep approach. Because of the steep approach, you might
need the drag that comes with full flaps.
- 2b)
- Your aim point will be not very far down the runway, so a
steep approach helps keep you within power-off gliding range. If you
lose power and need to glide a long ways, retract the flaps.
- 3)
- Increased incidence means that (other things being equal)
the pitch will be lower. (Remember: pitch + incidence = angle of
attack + angle of climb.) Extending the flaps makes it easier to see
over the nose but makes it harder to have the nosewheel in the air at
touchdown.
- 4)
- Increased washout increases roll damping so the airplane
handles more nicely near the stall.
- 5)
- In an ideal airplane, you would be able to make power
changes and configuration changes without perturbing the trim speed.
But in most airplanes, when the flaps are extended (and not
otherwise), every power change affects the trim. One of my students
pointed out to me that when I was flying with the flaps extended,
every time I moved the throttle I simultaneously nudged the trim wheel
with my thumb. I had been unaware that I was doing it, but it seems
like a very sensible habit. You know compensation is going to be
needed, so why wait?
- 6)
- Always glance at the airspeed indicator before reaching
for the flap handle. Make sure you are within the permissible speed
range.
Also note that in many light aircraft, the last notch
of flaps produces its full share of incidence and its full share
of drag, but has only a small effect on the stalling speed. Therefore
if you didn’t need the last notch for energy management on final,
you’ve got very little reason to extend the last notch at all,
unless the field is very short and you need to get rid of every
last knot of stalling speed.7
A gusty wind or a strong crosswind is a good reason
using less than full flaps. Compared to full flaps, reduced flaps
has the following consequences:
-
For any given airspeed8 you will touch down at a higher
pitch attitude. This means that if a gust during the “skimming”
phase (after the roundout) causes you to touch down a little sooner
than you intended, you will still touch down on the main wheels.
This is good, because the main wheels can take a much bigger
load than the nosewheel.
- By the same token: For any given pitch attitude
you will touch down at a higher airspeed. In most respects, touching
down at a higher airspeed is bad, but one might make the following
argument: Since the sideways force of the crosswind on the fuselage
is largely independent of your forward airspeed, and since your
rudder authority etc. are proportional to airspeed squared, touching
down at a higher airspeed gives you more authority to combat the
crosswind. Therefore, if you are worried about running out of
control authority, you might consider using less flaps, maybe
even no flaps. The tradeoff is that even a modest increase in
touchdown speed means you will use up significantly more runway.
You must take this into account.
- As mentioned above, the stall speed increases.
This is 100% bad. Even if you want a higher touchdown airspeed,
you still would like it to be as far as possible above the stall.
Remember that the effect of the flaps on the incidence
(retract = nose-high = usually good) is different from the effect of
the flaps on the stall (retract = bad).
Finally, while we are discussing configuration: extending the
landing gear is an important part of the landing configuration.
Please don’t forget this. Double-check it on short final.
12.7.3 Touch Down at the Right Point
In the presence of obstructions, a relatively steep approach will make
more of the runway available to you: Consider for example a 50-foot
tree quite close to the beginning of the runway. If you use a
six-degree approach slope, it will block you from using the first 500
feet of the runway. If you were to use a three-degree glide slope
instead, it would block twice as much of the runway. You can get
information about obstructions from the Airport/Facility Directory and
other sources. Also, whenever a runway has a displaced
threshold you should suspect it is
displaced because of obstructions.
If your airplane requires a 1000-foot landing roll, and you are
landing on a 2000-foot runway, you should arrange things so that you
use the middle two quarters of the runway. That gives you a
safety margin at each end. It doesn’t make sense to put all your
margin at one end or the other.
For an extreme short-field landing, your margins will be much smaller.
In this case, your touchdown point will be beyond, but only very
slightly beyond, the runway threshold. You must allow for the fact
that your aim point will not be the same as your touchdown point,
since the flare carries you forward several hundred feet beyond where
the a straight-line extrapolation of your approach path would go. The
correct procedure is to aim your approach path a corresponding
distance short of the intended touchdown point. In extreme
cases, the aim point may even be ahead of the runway threshold, as
shown in figure 12.16.
On any runway, long or short, pick a definite touchdown zone and hit
it as accurately as you can; don’t just land “somewhere” down the
runway. This shouldn’t be any extra work; it should be a natural
consequence of good aim-point control and good airspeed control, which
you need for other reasons.
|
Every landing should be a spot landing.
|
|
Pick a definite spot on the runway and land in the zone that begins at
this spot and extends 100 feet or so beyond, in normal conditions. If
you have unfavorable conditions (such as gusts, wind shear, and/or an
inexperienced pilot), the zone will be larger. Make sure the far end
of the zone leaves enough room for the rollout, plus a safety margin.
If the field is so horribly short that you need to choose an aim point
that is near the threshold, or ahead of it, choose a glide slope that
is steep enough that you can fly it without engine power. (Or, better
yet, go find a more reasonable runway somewhere else. At any field
where you can depart with reasonable safety margins, you should
be able to land with considerable margin at each end. See
section 13.7.2.)
At any field that is not horribly short, including any field where you
make a normal power-on approach, you should not locate your
chosen touchdown zone at the very beginning of the runway. There are
a couple of reasons for choosing a zone farther down the runway: (a)
it gives you more obstacle clearance, and (b) if you should ever have
engine trouble on final, you would have a much better chance of being
able to make a power-off approach to the very beginning of the runway.
I often fly at a rather short, obstructed field: 1700 feet after the
displaced threshold. That’s short but not too horrible; with some
skill and some headwind, you can land a Skyhawk using only half of the
runway. Some people are overly worried about running off the far end.
If you over-react to the possibility of an over-run, you might be
tempted to make an extreme short-field approach, so you would have the
largest possible amount of runway “left over” in front of you. But
that would be a bad idea, for the following reasons.
Much of flight safety
depends on margins and on backup plans. At every phase of flight you
should ask yourself how many things would have to go wrong at this
point before you would run out of options.
So why put all the safety margin at the far end? What about the near
end? Among other things, remember that hitting the ditch at the far
end when you’re almost stopped is better than hitting the ditch at the
near end at full flying speed.
So, a few years ago I decided that rather than using the first half
of the runway, I would use the middle half of the runway. This
reduced by half my margin against over-runs, but gave me vastly
greater margin against under-runs.
Sure enough, a few months after making that decision, I was with a
student who incapacitated the engine9 on half-mile final. At
that point we were close enough and high enough that I could glide
toward the weeds as shown in figure 12.16, flare, and land
on the runway with several inches to spare.
12.7.4 Touch Down at a Low Speed
If you land with too much groundspeed, you are in danger of running
off the end of the runway. I’ve seen this done on several occasions.
It tends to be embarrassing and expensive.
Excessive groundspeed can be due to a tailwind and/or excessive
airspeed. Sometimes the one can lead to the other, if you don’t
understand the basic principles of flight (chapter 7).
Here’s the scenario: Suppose you have a tailwind on final, and you
don’t realize it. Because the tailwind is carrying you along, if you
don’t do something, you are going to land too far down the runway. To
fix this, you unwisely push on the yoke and dive towards the aim
point. You may think this solves the problem, but in fact it makes it
worse. Now you’ve got too much airspeed (which contributes to a
too-high groundspeed) and the tailwind is still there (further
contributing to a too-high groundspeed).
Remember, it is OK to use the yoke as the up/down control
provided you are on the front side of the power curve and
you are willing to accept an airspeed excursion. On final
approach, neither of those provisos is true. Using the yoke as the
up/down control in such a situation is horribly improper pilot
technique. See section 7.3 for more on this.
Nobody intentionally lands with a tailwind. Nobody intentionally
lands with excessive airspeed. The problem is, all too often they
just don’t notice. Here is a list of things you can notice so you can
stay out of trouble. [AS] indicates airspeed cues, and [TW] indicates
tailwind cues.
-
[TW] As you approach the airport, listen on the radio and
make a note of which runway other airplanes are using. You can also
get wind information from ATIS, AWOS, and/or the Tower controller. As
you get closer, you can see which runway the other airplanes are
using. But remember that winds can shift, so the runway that had a
headwind a few minutes ago might have a tailwind now.
- [TW] Try to look at the windsock when you are on the
“downwind” leg of the traffic pattern. If your so-called
downwind leg actually has a headwind component, you’ve got a problem.
(Alas, it is often rather hard to see the windsock from traffic
pattern altitude, so don’t drive yourself crazy trying.)
- [TW] On the base leg, notice whatever wind-drift is
occurring. This is a really good source of information. Think about
this every time you fly the pattern. If you are being blown toward
the airport, that’s bad. Usually it means there will be a tailwind on
the runway. (In the rare cases where there is a headwind on the
runway but the base-leg wind is blowing you toward the airport, it
means there will be a tremendous windshear on final, which is a bad
thing unto itself, as discussed in section 16.17.3.)
- [TW] Every landing should be a spot landing. Even if you’ve
got a 7000 foot runway, don’t just land “somewhere” on the runway.
Pick an aim point, and keep that point a constant angle below the
horizon the whole time you are on final. This disciplined approach
gives you valuable information. In particular, you can observe how
hard it is to stick to the glideslope. If you’ve using the usual
configuration and the usual power setting, but the airplane keeps
floating above the glideslope, either you’ve got a tailwind, or you’ve
chosen an unreasonably steep glideslope. At this point you should
commit to not landing. Make a low pass down the runway so you can get
a good look at the windsock.
- [TW] Similarly, if you see an unusually large reading on the
Vertical Speed Indicator, it means you’ve got too much airspeed, or a
tailwind, or a too-steep glideslope angle, or some combination of the
above.
- [AS] Even more importantly, maintain a righteous airspeed on
final. Watch the crucial angles, as well as the airspeed indicator,
as discussed in section 12.5.
- [AS] If you touch down three-point, it is another sign that
you have too much airspeed.10 In a proper landing, the nose
wheel should be in the air. If you are afraid that raising the nose
would make you fly up into the air, go around (unless you are near
some huge obstructions). Since you have so much airspeed, the
go-around performance will be excellent: the airplane will leap into
the air.
- [AS] If you apply the brakes and get lots of squealing with
relatively little braking action, it is yet another sign that you’ve
landed with vastly too much airspeed. The problem is that the wings
are still producing lift, so there’s not enough weight on the wheels.
(See section 12.7.5.) You have got no business being on the
ground at this airspeed. Do not tolerate this. If you find flat
spots on your tires, it means a dangerously unskillful pilot has been
flying your plane.
- [TW] As you approach the runway for landing, you get another chance
to look at the windsock. If it is pointing the wrong way, go around.
Similarly, at a tower airport, if you say “wind check” the Tower
controller will tell you the current winds.
- [AS+TW] You might be able to perceive groundspeed directly. If
you think you’ve got an unusually high groundspeed, make a low pass
down the runway to double-check the windsock and other factors, then
return for landing. Perceiving groundspeed is hard. The perception
depends on altitude and other factors. I don’t know any good rules to
help you distinguish a good groundspeed from a bad groundspeed. It
may help to fly a downwind approach every so often, just so you can
see the difference. (Don’t land! And watch out for
opposite-direction traffic.)
In an airplane that normally touches down at 50 knots, you will use up
more than twice as much runway with a ten-knot tailwind than
with a ten-knot headwind. Roughly speaking, the amount of runway
consumed during rollout depends on the square of your
groundspeed at touchdown.
If the wind is so variable that it might switch from headwind to
tailwind at the last moment, make sure you have plenty of
available runway.
* Compensate for Density and Weight
Suppose you are flying at less than standard weight. For reasons
discussed in section 2.12.4, the angle of attack will be the
same but the indicated airspeed will be less. The percentage change
in speed should be half the percentage change in weight. If you fly
at the correct (lower) airspeed, you will use less runway. If you use
the uncorrected POH airspeed, you will use more runway than POH
tables indicate. The aircraft will tend to “float” more than it
should, because you arrived with the wrong angle of attack.
Now suppose you are landing at a high-altitude airport, where the air
density is less. For reasons discussed in section 2.12.3,
the angle of attack will be the same and the indicated airspeed will
be the same --- but the true airspeed will be greater, the vertical
speed will be greater, and the ground speed will be greater, by about
2% per thousand feet of density altitude. Because of the
groundspeed, you
will consume more runway, about 4% per thousand feet of density altitude.
Your POH should contain a chart or table with more accurate
information.
Note that in all cases, being able to accurately perceive the angles
is a big help.
* Compensate for Windshear and Gusts
Proper management of your airspeed during a short-field
approach is complicated and tricky. You have some difficult compromises
to make. A low airspeed gives you the best short-field performance,
but a higher airspeed gives you highly desirable protection against
stalling if there is a gust or a windshear (or a lapse in pilot technique).
Your Pilot’s Operating Handbook should specify the speed to use for
short-field landing. This is the indicated airspeed you want to have
when you begin your flare. In ideal conditions, you could trim for
this speed early in the final approach leg, and maintain this speed
all the way to the flare. In real-world conditions, however, the wind
makes speed management much trickier.
Therefore, you need to include the following steps
when planning your approach:
- Obtain an up-to-date estimate of the surface winds at the
airport. This could come from the ATIS, AWOS,
windsock, tower controller, other pilots, or whatever.
- Resolve the total wind into components, so you know what
headwind and crosswind to expect during landing. You can
use the methods of section 14.2.2, but rotate your
point of view so that you measure relative to runway heading, which
usually differs from your current heading (since you usually plan
the approach before turning onto final).
- Figure out what is the largest possible amount of airspeed
that you could lose to a sudden gust or windshear on short final.
(Gradual losses are no problem, and even sudden losses on long final
are a relatively minor problem.) Call this amount the “gust
allowance”. If it is larger than the headwind component, it means
you are faced with the possibility that the headwind could shear to a
tailwind, and therefore you should divert to a longer
runway; you don’t want to make a short-field landing with a
tailwind.
- Your airspeed on short final should be equal to the
short-field approach speed given in the POH minus a correction
for below-standard weight plus the gust allowance.
On final (as always!) trim for the appropriate speed and fly with a
light touch; this will greatly help you recognize when a windshear
occurs, as discussed in section 12.12.
If your approach speed includes a gust allowance
and the expected gust does occur, then you are in good shape.
Assuming you are at the right altitude and assuming you are not
expecting any further windshear, you can just raise the nose
and retrim. You are now flying at the handbook approach speed
just as if there had been no gust and no gust allowance. The
rest of the approach should be straightforward. (You typically
need to make a slight power reduction, because in the absence
of the headwind you will arrive at the runway sooner, so staying
on the glideslope requires less power.)
On the other hand, if the gust does not occur, you
will arrive at the runway with too much airspeed. Fortunately,
though, if you have followed all the steps above, the gust allowance
is less than the headwind component, so your groundspeed
is less than the calm-wind short-field groundspeed, and you if
you proceed to land your rollout shouldn’t consume any more runway
than it would in the calm-wind case.
The foregoing describes the correct procedure, in
which you anticipated the windshear. Let’s now consider various
situations that could arise if you have forgotten to include a
gust allowance in your approach speed.
1) Suppose you are flying at the handbook’s short-field
approach speed when a gust or windshear robs you of ten knots.
If this happens on long final, several hundred feet above the
ground, it is no big deal. You have lots of altitude and lots
of time. You can regain your airspeed by diving about 60 feet,
according to the law of the roller coaster (section 1.2.1).
At this point you are on a new glide path which is 60 feet lower
than the old one. This will take you to a point about 600 feet
short of where the old one would have (assuming a 6 degree glide
slope), but you can correct for this by increasing the power,
re-intercepting the desired glide path, and then reducing the
power.11
2) Now suppose you suffer a similar unanticipated loss of airspeed
when you are only 50 feet above the ground. In this case you have a
definite problem. At this point you are on (or below) the desired
glidepath and below the desired airspeed. You have a critical energy
shortage. You have nothing to gain by pulling back on the yoke; if you try it you are likely to
wind up as a statistic --- one more “unexplained” stall/spin
accident. The proper way to deal with it is to apply full power, as
discussed in section 1.4. Simultaneously, dive to
regain airspeed. Dive as much as you can without hitting anything,
and then proceed with a go-around. Do not attempt to salvage this
approach. Instead, go around and set up a proper
approach, including an allowance for the windshear.
|
Beware decreasing headwind on final.
|
|
12.7.5 Use the Brakes
To stop in the shortest possible distance, the procedure
is as follows:
-
Touch down on the main wheels as always,
- lower the nose wheel fairly soon thereafter,
- retract the flaps,
- apply the brakes, firmly but not skidding, and
then
- pull back on the yoke a little.
The reasons for these steps are as follows:
The amount of braking force that a tire can provide
is directly proportional to how much weight is on the tire. As
a consequence, you want to make sure there is as much weight as
possible on the wheels before applying the brakes. If the nose
is in the air, the wings are still supporting part of the weight
of the airplane. Lowering the nose reduces the angle of attack.
Retracting the flaps also reduces the angle of attack, since
it reduces the angle of incidence.12
A skidding tire provides much less braking force
than a non-skidding tire. You never have anything to gain by
allowing the tire to skid. Furthermore, skidding can very quickly
lead to loss of directional control. If you think the tires might
be skidding, release the brakes so they stop skidding, re-establish
directional control, then reapply the brakes.
In addition to the loss of braking effectiveness, skidding
is very destructive to the tires --- it quickly grinds away one part
of the tire. The loss of rubber shortens the life of the tire,
and the loss all from one place throws the tire out of
balance. An out-of-balance tire tends to hop off the
pavement, reducing braking and steering effectiveness.
The idea of pulling back on the yoke during braking
is simple: it increases the weight on the main wheels (which
is where the brakes are). The main wheels are now supporting
their normal share of the weight of the airplane, plus whatever
down-force is being developed by the elevator, plus whatever share
was previously being supported by the nosewheel. The idea is
not to lift the nosewheel off the ground, just to bring its share
of the weight almost to zero.
See section 12.6.4 for additional discussion
of the rollout, including the case of a not-very-short runway.
12.7.6 Summary: High-Performance Landing
For a short-field landing (compared to the basic
landing described in the previous section) ...
-
the aim point is short of the touchdown point.
- the approach is steeper.
- the airspeed is less (at corresponding points
throughout the approach and roundout).
- the skimming phase is shorter or nonexistent.
- you lower the nose wheel sooner.
- you apply the brakes sooner and harder.
These points can be seen by comparing figure 12.16
to figure 12.14.
12.8 Soft-field Landing
If the field is soft, it is important to touch down (1) as gently as
possible, with the smallest possible vertical speed, and (2) with the
lowest possible groundspeed. (In gusty-wind conditions, these two
objectives are somewhat in conflict, and the first one should get
priority. That is, it is better to touch down with a tiny bit of
extra horizontal speed, rather than to risk “dropping” the airplane
into the mire with any appreciable vertical speed.) If the field is
bumpy but not soft, the priority goes to touching down at a low
airspeed.
The key element of soft-field technique is to use engine power during
the flare and touchdown. This helps in two ways: first of all, the
propwash over the wings lowers the stalling speed, meaning you can
touch down at a lower speed, and secondly, the power allows you to fly
horizontally over the runway for an extended time, descending very
slowly, gently “feeling for the runway”.
The approach to a soft-field is basically the same
as a normal approach. The only differences are as follows:
On short final, after you are assured of reaching the field, you
should extend the flaps to get the lowest possible stalling speed.
Fairly late in the flare maneuver, you should add
a little bit of power, just enough to maintain level flight, or
a little bit less. The required amount of power is remarkably
small. You are in ground effect, so there is very little induced
drag, and you are moving slowly, so there is very little parasite
drag. If you add too much power, the airplane will speed up
or climb, which is not what you want. You will be much too busy
to look at the engine gauges during this maneuver, so use your
ears: you can learn to recognize the right amount of power by
its sound.
When the main wheels make contact with the ground,
friction will cause the airplane to slow down, possibly quite
rapidly. This friction will also create a torque that tends to
slam the nosewheel into the ground, so you generally have to pull
back on the yoke to prevent this. Also, you can anticipate that
the speed-change will drive your body forward (relative to the
plane) at just the moment where you want to be pulling back, so
tighten your shoulder harness and brace yourself.
As soon as possible after touchdown, reduce the power
to idle.
As always, when taxiing on a soft surface, keep the
airplane moving. If you stop, the airplane might sink in, and
you will be unable to get it moving again.
During the rollout, and during taxiing on rough surfaces,
it is usually a good idea to pull the yoke all the way back.
The remaining airspeed and/or the propeller blast acting on the
tail helps to reduce the weight on the nosewheel. This is important
because (1) the nosewheel is usually more vulnerable to damage
than the main wheels, and (2) more importantly, if the nosewheel
drops too heavily into a pothole it could result in a prop strike.
Here’s an advanced technique: if you are taxiing
toward an abrupt bump, such as the edge of a piece of pavement, keep
the yoke all the way back and apply
a blast of power during the few feet leading up to the bump.
If you do it right, in some aircraft the propwash hitting the
tail will allow you to “pop a wheelie”, lifting the
nosewheel almost (or perhaps entirely) off the ground. As soon
as the nosewheel is over the bump, reduce the power back to idle.
If you are based at a paved airport, the ideal way
to learn soft-field procedure is to fly somewhere that has a paved
runway and an unpaved runway. Land on the paved runway,
then practice soft-field taxiing and takeoffs before trying soft-field
landings. This way your first experience with a soft bumpy runway
comes at the lowest speeds rather than the highest speeds.
12.9 Crosswind Landing
Immediately before landing, the airplane is moving
through the air, and is hardly affected by the ground. During
the landing process and afterward, the airplane is moving along
the ground --- and is still affected by the air.
During the landing process and afterward, we want the airplane to be
moving straight down the runway, and we also want the axis of
the airplane to be pointing straight down the runway. These are
two separate requirements; especially in the presence of a crosswind
it is all too easy to have the airplane moving in one direction and
pointing in another.
The usual way to meet all the requirements is to land in a slip. (An
unusual alternative is discussed in section 12.9.5.)
Suppose for sake of discussion that the crosswind is coming from the
right. Early on final approach you observe that in order to keep the
airplane’s motion aligned with the runway, the airplane’s
heading is pointed a few degrees to the right.
This is normal, coordinated flight; the airplane’s heading is aligned
with the relative wind, i.e. aligned with the airflow. (For a general
discussion of how wind affects groundspeed and direction of travel,
see section 14.2.4.)
It is a very bad idea to touch down with the heading not aligned with
the runway. It will create a huge sideways force on the
landing gear, and could knock the
tires right off their rims. If the tires survive, they will create a
sudden large force in the direction you are pointing. This will cause
the airplane to scoot off the upwind side of the runway.13
12.9.2 Heading Control
You need to change the direction you are pointing so that it is
aligned with the runway, not the relative wind --- and you need to do
it without changing the direction you are going. Use the pedals
(the left pedal in this case) to aim the nose at a point on the
centerline at the far end of the runway. Keep it pointing there.
This yaw task is simple, because it is almost independent of what you
are doing with the bank angle and the pitch angle. If you see a
nonzero yaw angle (relative to runway centerline), fix it right away,
using the rudder.
12.9.3 Drift Control
Using rudder alone might work for a moment, but it won’t work for
long, because the wind is now striking the side of the fuselage and
blowing the airplane off course --- an undesired boat turn (as
discussed in section 8.10). To solve this problem, lower the
upwind wing. This tilts the lift vector toward the upwind side,
providing a force that counteracts the wind on the fuselage. The rule
here is fairly simple: You use the bank angle to get rid of left/right
drifting motion.
If the crosswind suddenly increases (as it so often does), or if you
have selected not quite enough bank angle, the airplane will start
drifting to downwind. By the time you notice this, you’ve got three
different problems that need to be dealt with separately. (1) Obviously
part of the task is to increase the bank to correspond with the actual
amount of crosswind. That is, in the long run you want to have zero
sideways force on the airplane. (2) However, in the short run that
doesn’t suffice. With zero force, the airplane will continue to
drift, in accordance with Newton’s first law
(section 19.1). So
temporarily you need even more bank. Later, after you have brought the
drift velocity to zero, remove this extra bank. To summarize: you
need some bank in proportion to the crosswind (whether you’re drifting
or not) and you need some bank to arrest the drift rate (no matter
what the actual crosswind is).
The timescale during which left/right momentum builds up is, alas,
comparable to a student pilot’s reaction time, which can lead to wild
oscillations. If you find yourself overcontrolling left/right, get
away from the airport and practice slipping along a road
(section 16.9) until you get a feel for how the
airplane responds.
(3) You care about left/right position, not just velocity. If you
have drifted off to one side, you should set up a slight drift back
toward the centerline. Don’t be in a big hurry; the smoothest
correction is better than the quickest correction. (If you are so far
off that a radical correction seems necessary, go around.) Also
remember that the airplane has lots of inertia, so it will take a bit
of effort to get the corrective drift started, and it will take a bit
of effort to get it stopped as you approach the centerline. (See
section 16.9 for more on this.)
12.9.4 Flare and Touchdown
You are now ready to touch down. Land on the upwind wheel. Land on
the upwind wheel!14 You
should keep the ailerons and rudder deflected even
after touchdown. Keep rolling along on one wheel for a while; as the
airplane slows down you will need to apply more and more aileron
deflection in order to maintain the bank angle.
Remember, you need that bank angle to provide the force that resists
the wind.
|
Land on the upwind wheel.
|
|
Only after the upwind wheel has considerable weight on it should
you allow the downwind wing to settle. At this point the aircraft
is no longer banked. The friction of the wheels on the runway
is the only force resisting the
sideways force of the wind. The
amount of sideways friction a tire can produce is proportional
to the weight on it, which is why you must not level the wings
until there is plenty of weight on the wheel(s).
Do not neutralize the ailerons. The crosswind is constantly trying to
flip the airplane over onto the downwind side. Keep the ailerons
deflected to combat this. It doesn’t hurt to slightly overdo it,
keeping a little extra weight on the upwind wheel. As airspeed
decreases, you will need progressively more aileron deflection to
create the required amount of force.
To reiterate, the overall sequence should be:
-
Lower the upwind wing and apply downwind rudder.
- Land on the upwind wheel.
- As the lift dies away, the weight of the airplane will force
the other main wheel onto the ground.
- Then you can let the nosewheel come down.
During this whole process you need to maintain pressure on the
downwind rudder pedal, to counteract the weathervaning tendency
(section 8.11). As soon as there is weight on the
nosewheel, the nosewheel steering becomes effective, adding to
whatever steering the aerodynamic forces on the rudder have been
providing. Therefore at this point you can expect to suddenly need
somewhat less pedal deflection.
Maintain appropriate aileron and rudder deflection during the
rest of the rollout, and during taxiing as well. Remember, the
flight isn’t over until the airplane is tied down.
The question arises: at what point should you make the transition
from coordinated flight (on final) to slipping flight (for touchdown)?
Some pilots prefer to establish the slip on short final or even
earlier; the idea is to have time to get the “feel”
of the slip. My recommendation, though, is to begin the slip
at the same time you are beginning the flare, not much earlier.
The rationale is: (1) A strong crosswind is usually accompanied
by a considerable headwind component, delaying your arrival at
the runway, in which case an early slip is the last thing you
need. It just creates drag which steals energy and aggravates
the tendency to land short.15 (2) The winds near the ground are never
the same as the winds aloft, so any slip established on final
will have to be changed during the flare anyway.
Be sure to correct for whatever crosswind is actually there at
each point, not the crosswind you were expecting. Crosswinds are
notoriously variable. As you descend and as you travel down the
runway, you move in and out of the lee of trees and buildings.
If the crosswind is really strong and/or variable, you might consider
using less than full flaps, as discussed in section 12.7.2.
There are some exceptional cases where landing on the upwind wheel is
not recommended. An example is a late-model Boeing 737, which has a
relatively narrow wheelbase, and huge engines mounted below the wing.
You have to land with the wings level; otherwise one engine would hit
the ground. A similar situation arises with certain amphibian
aircraft that have outrigger-type floats or sponsons far from the
centerline.
You begin by maintaining coordinated flight as long as possible. The
direction of motion will be aligned with the runway, but the heading
will not, until the very last moment. Then, use the rudder to align
the heading with the direction of motion. Deft aileron usage is
needed to maintain wings level during the yaw maneuver, because of the
unequal wingip velocity. The remaining few seconds of flight will be
a wings-level slip. This will begin a wings-level boat turn,
but you hope not to turn very much. The idea is to touch down before
the sideways force imparts any significant sideways velocity. This
technique is not recommended for typical general-aviation aircraft.
It’s more work than necessary, and in a light aircraft the sideways
velocity builds up too quickly.
12.10 Going Around
Before you begin the approach, at the time you review the landing
checklist, be sure to review the go-around checklist.
If you’re not prepared for the go-around,
you’re not prepared for the approach.
|
|
There are many situations that call for a go-around. You should think
about this in advance and establish guidelines for yourself so that
you can begin a go-around immediately when the need arises.
If you need to go around, don’t wait until the last moment. If you
are rolling toward the end of the runway and are worried about running off
the end into the trees, attempting a go-around will only make it
worse. It is better to hit the trees when you are almost stopped than
to hit the trees with almost enough energy for a go-around. An early
go-around is good, but a late go-around is worse than nothing.
Here are some guidelines. You can imagine exceptions; for instance
if you are flying a glider it is hard to perform a go-around. So you
should come up with guidelines adapted to your situation. The point
is that you should think about the go-around decision in advance. The
accident records contain many examples of people who got into trouble
because they spent too long deciding whether or not to go around.
- If you think you might be too high and/or too fast to land
within the predetermined zone as mentioned
section 12.7.3, go around. Do not try to “salvage”
the approach by using extra runway.
- If your attempted landing results in a bounce, go around.
Many accidents start with a harmless bounce; the salvage attempt
results in running off the runway or making a disastrously hard
landing.
- If there is a possibility of tailwind, make a low pass to
check out the windsock, then return for landing.
- If there is a possibility of wildlife on the runway, make a
low pass to scare them off, and another to make sure they are gone,
then return for landing.
- If the crosswind is so strong and/or gusty that you have
doubts about being able to keep the airplane on the runway, go
around. Indeed, don’t just go around, go away. Find another runway
that is wider and/or more aligned with the wind.
- If another airplane pulls onto the
runway when you are on short final,16 break to one side and go around. Do not
stay on the centerline; break to one side so you can keep an eye on
the situation, since the other airplane remains a collision threat
even while you are going around. Do not try to land farther down the
runway (hoping that the other pilot will hold in position). Do not
try to land short (hoping that the other pilot will take off and get
out of your way).
- On an instrument approach, if you can’t see the runway at
certain predetermined points, a go-around is mandatory.
- If you find yourself on final with the landing gear not down
and locked, or otherwise find yourself not in the correct landing
configuration, go around. This is usually a sign that you didn’t
follow the landing checklist, and you need to take the time to
re-run the whole checklist, to see what other things you may
have missed.
- Do not wait until you are sure you need a go-around; that’s
the wrong question. The right question is whether you are sure
things are OK for landing. If you are unsure, go around.
- If ATC says go around, go around. If your copilot or
instructor says go around, go around. If you disagree, go around
and argue about it later. (There are exceptions; don’t let yourself
get talked into attempting a dangerously late go-around.)
If ATC clears you to land, that does not prohibit
you from going around. For instance, if your gear is not down,
ATC would prefer to see you go around rather than land gear-up.
Similarly, if ATC clears you to “land and hold short” of a runway
intersection, they would prefer see you go around early rather than
skid through the intersection at the last moment.
Energy mismanagement is the most-common reason for go-arounds. This
is a good reason for evaluating your energy situation early and often.
Ask yourself: are we high and fast, or low and slow? Fixing an energy
problem is easy if you start early, but it is hard or impossible if
you start late. Also remember:
An early go-around is good, but
a late go-around is worse than nothing.
|
|
When you begin the go-around, do it right. Don’t add “some” power;
add full takeoff power.
In a Cessna 152, 172, or 182 with flaps extended, an
increase in engine power will magically re-trim the airplane for a
lower airspeed, as mentioned in section 2.3. This is annoying
when you make small power adjustments on final approach, and downright
dangerous when you apply full power for a go-around. Your first
defense (which works in all airplanes) is to watch the pitch attitude;
if the nose wants to pitch up, don’t let it. Push on the yoke as
necessary to keep the pitch where you want it. This is sometimes
quite a hefty push. (Practice simulated go-arounds at a safe altitude
every so often, so you won’t be surprised.)
Take a look at the airspeed indicator. Raise or lower the nose as
necessary to establish the proper airspeed for the go-around.
After you have done the right thing with the power and the angle of
attack, start working on the configuration. If you are carrying full
flaps, remember that the last notch contributes a lot of drag but
doesn’t contribute much to the stalling speed, so you want to retract
that notch fairly early in the process. Also, retracting the flaps
part way will help with the trim problems. Don’t retract the rest of
the flaps until you have a reasonable airspeed margin above the stall.
To the extent possible, use the trim wheel to take the pressure off
the yoke. (A yoke-mounted electric trim switch comes in very handy for
this.)
Make sure you have established a positive rate of climb before
retracting the gear. This rule arises because in some situations you
may need to perform a “bounce and go” --- that is, to touch down on the
runway briefly before going around. It is much nicer to bounce on the
wheels.
12.11 Learning to Land the Airplane
12.11.1 Maneuver by Reference to the Edge
As mentioned in section 12.6.2 and section 12.2,
in most airplanes, the pilot cannot see the runway centerline
when the airplane is the proper attitude for touchdown. This
comes as a shock to many student pilots.
Therefore, we want to land on the center line by reference to the
edge line.
There are several good ways to learn to do this. Repeated
out-of-control attempts to land the airplane are not the recommended
way.
A trick that works beautifully in typical light Cessnas
(150/152/172/182)17 is the following: taxi down to the end of a disused runway
(e.g. the crosswind runway) or a long taxiway that resembles a runway.
Taxi into “takeoff position” and shut down the engine. You remain
in the left seat, while your instructor sits on the tail,
raising the nose to touchdown attitude.
You should sit there for several minutes contemplating the
perceptions. Compare level attitude with touchdown attitude. You
will note that in touchdown attitude, you will not be able to see the
centerline or the right-hand
edge of the
runway, but you will be able to see the left-hand edge. Especially if you move your head a little toward your
side of
the airplane, you should be able to see the whole sideline --- from
the point abeam your position all the way to the far end.
You can study these perceptions during taxi. Fortunately,
all landings are preceded by takeoffs. Especially in an unfamiliar
airplane, you should consciously use the pre-takeoff taxi to practice
taxiing on the centerline without looking at the centerline.
That has a certain Zen ring to it, doesn’t it? The trick is to
taxi by reference to the taxiway edge line on your side. If the
taxiway is 40 feet wide, you should concentrate on taxiing 20
feet in from the left edge. The instructor may help by holding
a chart in front of your nose, forcing you to control the airplane
by reference to the sideline.18 Every ten seconds or
so the chart will be moved aside so you can recalibrate your perceptions.
During taxi, you should also practice perceiving height. Ask
yourself, “how far below me are the wheels?” You will need to know
that when it comes time for landing.
12.11.2 Hesitation Takeoff
Make sure you have an instructor with you, especially the first time
you try this. At an airport with a nice long runway, taxi into
position for take-off. Pull the yoke all the way back, as you would
for a soft-field takeoff. Using full power temporarily, speed up
until the nose comes up to the attitude that corresponds to stalling
angle of attack or slightly less. Then retard the throttle almost to
idle so that your airspeed does not increase any more. Do not let the
pitch attitude or the airspeed get so high that you actually become
airborne. Do not raise the nose so much that the tail hits the
runway. Then just taxi down the runway in this configuration. Make a
careful note of the perceptions of height, pitch, heading, and
left/right position relative to the edge line.
Make sure you don’t run out of runway. One option is to close the
throttle, stop, and taxi back. Another option is to add power and
fly away. Be careful to maintain constant pitch attitude as you
increase the power. This will require releasing some of the back
pressure on the yoke, since the increased propwash
increases the effectiveness of the tail.
12.11.3 Practice Maneuvering at Altitude
The traditional (but not the best) way to learn about
landing the airplane is try it again and again until it comes
out right.
Landing practice has its place, of course --- but it
is not the only thing, or the first thing, you should do. Especially
if you are learning landings for the first time, or are learning
to fly a new type of airplane, there is no point in practicing
defective landings over and over. That just reinforces bad habits.
Also, as Langewiesche (reference 1) pointed out, landings
happen so quickly that there is very little time to learn anything.
Therefore, you should leave the traffic pattern. Go somewhere
where you have more altitude and fewer other aircraft. Perform the
familiarization exercises as described in section 16.10.
You want to spend a fair amount of time practicing slow flight. This
is the sort of thing you really want to learn in the practice area,
not during an attempted landing. Landing involves flying very slowly,
right next to the ground. You’ve got no business trying to fly slowly
at three feet above ground level (AGL) if you don’t know how to do so
at three thousand feet AGL.
In slow flight, in the landing configuration, make a note of the angle
of attack. This is the angle of attack you want to have when you
touch down on the runway. Remember the pitch attitude that goes with
this angle of attack. Observe the angle the cowling makes relative to
the forward horizon, and observe the angle the wingtip makes relative
to the lateral horizon. Since at touchdown you will be (I hope)
flying purely horizontally (i.e. negligible vertical velocity), the
pitch attitude tells you everything you need to know about the angle
of attack (at any given flap setting).
You will probably discover that the angle of attack
you want to have on final approach is halfway between the cruise
angle of attack and the stalling angle of attack. This rule of
thumb is related to the more widely known rule of thumb that approach
speed should be about 1.3 times the stalling speed.19
This little fact (approach angle of attack is halfway between cruise
angle of attack and stalling angle of attack) is more useful than it
might seem. It means you can land the airplane --- and I mean an
on-the-numbers, short-field landing if necessary --- even if your
airspeed indicator has failed (or you just can’t see it because your
lights have failed at night). You should not consider yourself
properly “checked out” in an airplane until you know how to do this.
Table 12.1 shows some airspeeds and angles for
a typical general-aviation aircraft.20
| |
Airspeed (KCAS) |
Pitch Attitude |
Incidence |
Angle of Climb |
Angle of Attack |
| cruise (clean) |
115 |
0.0° |
4.5° |
0.0° |
4.5° |
level VY (clean) |
76 |
4.0° |
4.5° |
0.0° |
8.5° |
| level (flaps) |
76 |
0.0° |
8.5° |
0.0° |
8.5° |
| slower (flaps) |
70 |
2.0° |
8.5° |
0.0° |
10.5° |
descent (flaps) |
70 |
-2.0° |
8.5° |
-4.0° |
10.5° |
| flare (flaps) |
decr. |
incr. |
8.5° |
incr. |
incr. |
| stall (flaps) |
53 |
12.0° |
8.5° |
0.0° |
20.5° |
On approach, the angle of attack is distinctly not the same as the
pitch attitude. Don’t be fooled; bear in mind that you probably have
ten or a hundred times more experience in level flight than you do in
descending flight. You’re not flying toward the horizon any more;
you’re flying toward a point several degrees below the horizon. As
you transition from level flight to a four degree descent, you need to
lower the nose by several degrees in order to maintain the same angle
of attack.
12.11.4 Practice Flaring and Stalling at Altitude
The following is a great way to learn some of the
skills that you need for landing the airplane.
Choose a safe altitude (3000 feet AGL or thereabouts)
and designate it as the altitude of a “virtual runway”.
Starting at an altitude 500 feet or more above the virtual runway,
set up a power-off glide in the landing configuration (gear and
flaps extended) at the normal approach speed. Then, about 10
feet above the virtual runway, begin a flare, so that you wind
up flying level, power off, at the virtual runway altitude. As
the airplane slows down, keep pulling back, cashing in airspeed
to pay for drag, maintaining altitude. Continue pulling back until
the airplane stalls. Then make a normal stall recovery.
The point of this maneuver is to learn at what rate
you need to raise the nose during the flare to maintain level
flight.
As a variation of the above procedure, you can practice
“soft field” landings on the virtual runway. After
you have flown horizontally at the virtual runway altitude for
a second or two with zero power, add enough power to sustain steady
level flight. See also next section.
Practice recovering from evil zooms (section 12.11.8) and
other types of defective flare (section 12.11.9).
12.11.5 Practice Flying in the Runway Environment
As mentioned above, the
landing flare lasts only a few seconds, and if you do a hundred
landings you still have only a few minutes of experience handling
a flaring airplane. Practicing slow flight at altitude is a tremendous
help. Practice this. However, don’t expect it to do the whole
job, because (a) the airplane handles slightly differently in
ground effect, and (b) you need to learn to perceive alignment
with the runway, altitude, descent rate, etc. very precisely,
based on visual cues in the runway environment.
Before actually trying to land the airplane, go to
an airport with a nice long runway and make a few low passes at
a safe airspeed.
-
1)
- Make the first pass about 10 feet above the runway
at approach speed.
- 2)
- Then try it about 5 feet above the runway, at
approach speed.
- 3)
- As you gain skill and confidence, try it about
2 feet above the runway, at approach speed.
- 4)
- Then try it about 1 foot above the runway, at
approach speed.
During these maneuvers, you will learn to judge your
height above the runway, learn to maneuver the plane so that it
is centered on the runway, and learn to use the rudder (and opposite
aileron) to get the fuselage aligned with the direction of motion
even in the presence of a crosswind.
Finally, after you know how to perceive and control
what is happening in the runway environment:
-
5)
- Fly down the runway one foot or less above the
surface, at a low airspeed. This will be discussed at length
in the next section.
Note that it is a very, very bad idea to fly
10 feet or even 5 feet above the runway at a low airspeed. It
is OK to stall the airplane at 3000 feet AGL, and it is OK to
stall it at 0.5 feet AGL, but it is definitely not OK to
drop it in from 10 feet AGL.
12.11.6 Learn Soft-Field Procedure First
After you are comfortable with high-speed flight in the runway
environment, and with flaring the airplane at altitude, and handling
it in the touchdown attitude, it is time for the most important
exercise.
Fly the approach to a nice long runway. As you flare, advance the
throttle a tiny amount. The idea is to generate enough power to
allow you to fly down the runway in ground effect, a small distance
above the ground. This is the soft-field landing procedure, but
it works just fine on paved runways, too.21 Strive to maintain one foot of altitude. You should
be able to hold this altitude within a few inches. As you become
more proficient, try maintaining ever-lower altitudes with ever-finer
precision.
The amount of power required is very small, perhaps only 100 RPM above
idle. Because the airplane is in ground effect,
induced drag is greatly
reduced. Because the airplane is moving so slowly, parasite drag is
very small.
Gradually raise the nose to the proper touchdown
attitude, and keep flying down the runway at “zero point
five AGL”. If a gust comes along and drops you the last
six inches, it will be a perfect landing.
Remember to keep a careful watch on the runway edge;
in the proper touchdown attitude you won’t be able to see the
centerline and if you persist in trying to look out the front
you will wander off to one side and mow down the runway lights.
Also, keep your wits about you --- don’t fly the whole
length of the runway and run into the trees at the end. Make
a timely decision to add power and go around, or chop the power
and land.
Take the time to look down at the runway, to double
check your perception of height. Look at the lateral wingtip
against the horizon. Get rid of the notion that the landing is
something that happens at a point in time. Landing is a process
that lasts a goodly amount of time.
12.11.7 Nose-High Rollout
After landing, the nosewheel is supposed to stay in the air for a
while. For practice, you can make it stay in the air quite a bit
longer by adding a
tiny amount of power. That creates a situation analogous to the
hesitation takeoff described in section 12.11.2.
Even if you don’t add power, try to keep the nosewheel off the ground
for as long as you can (provided you’ve got enough runway). This has
two advantages.
-
When the nose is up in the air, the airplane produces
relatively high drag. This called aerodynamic braking. It
allows you to slow down without wearing out the brakes.
On the other hand, aerodynamic braking is not as effective as real
brakes, so if you are approaching the end of the runway, lower the
nose and retract the flaps. This puts more weight on the wheels, and
therefore allows you to apply the brakes more heavily without
skidding.
- This provides additional practice handling the plane in the
proper touchdown attitude. You should try to learn from every
landing.
Another suggestion: You will sometimes (alas) touch down with a
too-low nose attitude, so that the nosewheel hits almost immediately.
If this happens, gently raise the nose to the proper attitude. Again,
the purpose of this is twofold: aerodynamic braking plus a reminder
of what proper touchdown attitude looks like. If this causes you to
become airborne again, it means that your touchdown speed was much
too high, which is a valuable lesson. Just stop raising the nose,
wait half a second, and the airplane will re-land.
12.11.8 Recovering from an Evil Zoom
Consider the situation where you flare too much,
too late. That is, you fly down quite near the ground and, while
your airspeed is still several knots above the stall, you pull
back on the stick quite a lot. The pitch attitude will become
very much nose-up. If you allow this pitch attitude to persist,
the airplane will zoom up a few feet and then stall. At this
point, there is no way to prevent a crash. The usual stall-recovery
procedure (diving to regain airspeed) will not work. You won’t
be able to dive enough, because the ground gets in the way.
This is a common and very serious mistake. It is a particularly evil
type of zoom. (Some other books call it “ballooning” but that seems like
an insult to all the beautiful hot-air balloons and helium balloons in
the world.)
Obviously you want to stay out of situations from which no recovery is
possible. The solution in this case is simple: you absolutely must
observe the pitch attitude.
If you see
a large nose-up pitch attitude, begin a recovery immediately. Do not
wait to hear the stall warning horn. Do not
wait to feel aerodynamic indications of a stall. Push the nose back
down to the attitude that corresponds to slow flight (roughly 15
degrees nose up in typical airplanes) and apply full power
immediately. You know that the airplane can fly level at full power
in this attitude, so if achieve that attitude and that power setting
soon enough (before you have lost too much airspeed) you will be fine.
It is important to practice this procedure, as discussed in section 16.20.6.
Do not try to salvage the landing. Go around!
You cannot recover from an evil zoom simply by reversing
the process that got you into trouble. During the upward zoom and
the downward “reverse zoom”, the airplane loses so much
energy due
to drag that you will not be able to arrest the descent in time
for touchdown. To say it again: If you see a bad nose-up situation
and try to recover just by pushing the nose way down, the airplane
will dive right into the runway nose-first. This is an example
of a pilot-induced oscillation, as discussed in section 16.4.
You can reduce your chance of falling prey to an evil
zoom by thinking about the pitch attitude at all times. You need
to control attitude in the short term, as a means of controlling
altitude in the long term.
12.11.9 Salvaging an Imperfect Flare
Nothing is perfect. Sometimes the flare is noticeably imperfect, yet
not so bad that a go-around is required. The number of possible
imperfections is enormous, so we can’t discuss them all, but it is
worth discussing how to handle the most-common cases.
Remember that for any given airspeed on short final, there will be
exactly one ideal altitude at which to begin the roundout, and one ideal
rate at which to raise the nose.
Scenario #1: Suppose you begin the roundout a little bit too
late, and/or raise the nose too slowly during the initial moments of
the roundout. You can detect this by noticing that the ground is
rushing up toward you and will reach you too soon.
Solution: Raise the nose at a slightly higher rate than usual, fast
enough to arrest the descent in the available time. This results in
an almost-nice roundout, just a little bit squared-off. At best, this
salvaged flare will end at a point where you have the right altitude
(a few inches) and the right vertical speed (zero), at the cost of
having too much airspeed. If there is enough runway available, just
skim along until the airspeed bleeds off, then touch down. On a short
runway, don’t attempt to salvage this scenario. Go around --- the
sooner the better.
Scenario #2: Suppose you begin the flare at about the right
time, but you raise the nose at too great a rate during the first
part of the roundout. (This can be considered a very mild version of
the evil zoom discussed in the previous section.)
Solution: If you notice this early enough, you can salvage the
situation. You should temporarily stop raising the nose. Hold a
constant pitch attitude for a few moments. This constant pitch
attitude will not correspond to a constant airspeed, nor a
constant angle of attack, nor a constant vertical speed. The airplane
will lose energy, lose airspeed, and develop an ever-increasing rate
of descent. You may think that lowering the nose is the “obvious”
way to undo the error, but you should resist the temptation; by the
time you have manage to lower it, you will be at too low an altitude
with too great a descent rate. Therefore, just hold a constant pitch
attitude. Adding a smidge of power (a) will keep things from
happening too fast, and (b) means you will have more energy at the end
of the roundout. (If you add too much power, then at the end of
the roundout you’ll have more energy than you need, causing prolonged
skimming as discussed in the previous scenario.) As you fly along at
constant pitch attitude, at some point you will see a combination of
airspeed and descent rate that you recognize from your previous normal
landings. At that point, resume raising the nose at an appropriate
rate.
Scenario #3: Suppose you begin the flare too early. Your first
indication that something is wrong might be the
following: You are flying a nice circular looping path that will be
tangent to the ground; that is, you will reach zero altitude at just
the time you reach zero vertical speed. However, alas, you notice
that in order to do that, you are raising the nose at a rate that will
lead to a stall before the roundout is completed.
Solution: Add a little bit of power. During the rest of the maneuver,
raise the nose at a reduced rate. (Once again, if you add too
much power, it could eat up a lot of runway.)
12.12 Fly with a Light Touch
As discussed in section 2.7, it is vitally important to
be aware of how much force you are putting on the yoke. This is good
practice in all regimes of flight, but it is particularly important on
approach. In particular, imagine you are conducting a short-field
approach, which means you’ve got no excess airspeed. Suppose on long
final everything is just right: the right direction of flight, the
right pitch attitude, the right angle of attack, the right airspeed
--- and in particular, the right trim.
You can --- and should --- confirm that you’ve got the
right trim by letting go of the yoke.22
Now suppose that on half mile final the airplane spontaneously pitches
down.
The airplane is trying to tell you something! It is trying to tell
you that it lost some airspeed --- presumably
because of a windshear. This is a
very, very common thing to
happen on final. You are presumably landing into the wind, and
the headwind is almost certainly stronger at pattern altitude
than it is on the ground. Therefore you are virtually guaranteed
to encounter a decreasing headwind during the final descent.
This will rob you of some airspeed. If you are lucky, it will
happen so gradually that nobody notices. If you are not lucky,
it will happen suddenly. A few knots will suddenly disappear from the
airspeed indicator (which you may not notice) and the airplane
will want to pitch down (which it is your duty to notice).
The all-too-common temptation is to pull back on the yoke, trying to
maintain pitch attitude and (vainly) hoping to maintain constant angle
of descent. This is not smart.
Remember: the airplane is trimmed for a definite
angle of attack. If you pull back on the yoke, you are forcing
the airplane to a higher angle of attack (and a lower airspeed).
Since you were already trimmed for short-field approach speed,
this is definitely not a good idea.
To reiterate: the yoke is not just a control carrying
commands from you to the airplane --- it is also a valuable sensor
carrying information from the airplane to you.
With rare, brief exceptions, you
should keep the airplane trimmed for the desired airspeed (or, rather,
angle of attack). You should be aware of (and wary of) any force you
apply to the yoke, forcing the airplane off its trim speed.
Additional discussion of airspeed management, including compensation
for windshear, can be found in in section 12.7.
12.13 Critique Your Own Landings
Some of my students learn faster than others. The
ones that learn the fastest are the ones who have internalized
a set of high standards (and even higher goals) and who have learned
to critique their own performance. These folks give me a good
feeling. I know that they will continue to get better even when
I’m not in the plane --- a pleasant contrast to those who get gradually
worse when left to themselves, and depend on the instructor to
get them back in shape.
The standards for a good approach and landing are
reasonably easy to remember:
-
Review the checklist before the approach. Make
sure you are prepared for the approach, the landing, and the
go-around.
- Use the right configuration (flaps, landing gear,
carburetor heat, cowl flaps, et cetera).
- On final, track the extended centerline. (That
is, don’t just fly toward the threshold at some cockeyed angle.)
- On final, maintain the correct angle of attack.
Flying with a light touch will help you with this.
- On final, maintain a constant angle of descent.
That is, keep the aim point a constant angle below the horizon.
- Pick a definite spot along the runway. Pretend
it is the beginning of a very short runway, and try to land beyond,
but less than 100 feet beyond, that spot.23
- At touchdown, the nosewheel should definitely
be in the air.
- The touchdown should be gentle enough that the
nosewheel stays in the air during touchdown and during
the first 50 feet of the rollout.
- At touchdown and thereafter, the axis of the
airplane and its direction of motion should be aligned
with the runway. In a crosswind, this means landing on the upwind
wheel.
- At touchdown and thereafter, the airplane should
be sufficiently well centered that the centerline is between the
main wheels.
- Don’t (accidentally or otherwise) apply the brakes
until there is plenty of weight on the wheels.
- Stay in control during the rollout.
If you can do all those things, you don’t need an
instructor to tell you it was a good landing.
- 1
- If you are staying in the traffic pattern, doing
touch-and-goes, you must brief the landing checklist
before takeoff.
- 2
- To
calibrate your thumb, you can use the following rather specialized
facts: The standard face-plate on a household light switch is
4.5 inches tall. At a distance of 5 feet, 4 inches, it subtends
four degrees. Therefore, measure the switch (just to make sure)
and then stand with your eye 5’4” away and see how your thumb
compares.
- 3
- By the way, you should make sure your line
of sight to the threshold is unobstructed. At night, if the green
threshold lights are blinking or can’t be seen at all, it tells you
there is an obstruction between them and the airplane. Add power!
- 4
- Extending the flaps will help.
A booster-cushion on the seat may help. A modest slip
might help you see past the side of the nose. A landmark
abeam the aim point often comes in handy. If the problem is
severe, you might want to choose a different model of airplane.
- 5
- Of course this angle
is not exactly
constant; it depends on flap setting, it depends on whether your
seat is adjusted extra-high or extra-low, and it depends on the
amount of headwind.
- 6
- Obviously this discussion does not apply to tail-wheel
type airplanes.
- 7
- A student
pilot might be tempted to always extend full flaps so that all
landings would have the same incidence and would therefore look
the same, but a sophisticated pilot should be able to deal with
the difference between full-flap and partial-flap touchdown attitudes.
- 8
- This
applies to airspeeds that you can actually achieve, without stalling,
at the reduced flap setting.
- 9
- In a Cessna, if you pull
the throttle all the way out and then bend it down, it’s stuck
at idle and you can’t fix it without tools.
- 10
- This applies to ordinary
nose-wheel aircraft, not taildraggers.
- 11
- If your previous aim point
was halfway down a long runway, you could just choose a new aim
point 600 feet ahead of the old one, but you should feel guilty
about doing so. If you ever have to choose a new aim point, you
should take it as a warning of poor pilot technique.
- 12
- On
some airplanes, the flap handle is distressingly close to the
landing gear handle. Make sure you grab the right one. You don’t
want to retract the landing gear by mistake.
- 13
- You
might think the wind would always blow airplanes off the downwind side
of the runway, but more often than not they end up on the upwind
side.
- 14
- It is a common mistake among beginners to
roll the wings level just before touchdown (even though they had been
maintaining the correct slip up to that point) --- perhaps in the
effort to make it “look like” a normal no-crosswind touchdown.
- 15
- Also:
Heaven help you if try to “stretch the glide” by pulling
back on the yoke. If you stall out
of a slip you will enter a spin, and there will not be enough
altitude for a recovery.
- 16
- If that happens on long
final, don’t over-react.
- 17
- It doesn’t work as easily
on Pipers, because they require much more force on the tail to raise
the nose.
- 18
- While
you are looking out the side, make a note of how
the wingtip looks against the lateral horizon. That is provides
very useful pitch and bank information.
- 19
- As discussed in section 2.12.6,
you must multiply the calibrated (not indicated) stalling speed by
1.3, and then convert the product to an indicated airspeed.
- 20
- For
other, similar aircraft, the numbers will be similar. In a radically
different type of airplane (e.g. a jet interceptor with short,
highly-swept wings) the numbers will be radically different.
- 21
- As
discussed in the previous section, do not attempt this maneuver
until you are proficient at judging altitude and maneuvering in
the runway environment. Do not do anything that puts you at risk
of a low-altitude stall until you are within a foot or so of the
runway.
- 22
- Don’t
take your hand away and start scratching your ankle; just open
your grip to the point where you are not quite touching the yoke.
- 23
- On
a long runway, on a day with gusty crosswinds, this is the least
important of the criteria. I’m willing to compromise a little
on spot-landing performance if necessary to get a soft, slow,
well-aligned touchdown.
[Previous]
[Contents]
[Next]
[Comments or questions]
[Marketing Needed -- Can You Help?]
_
Copyright © 1996-2005 jsd