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Pilot's Handbook of Aeronautical Knowledge
Aircraft Performance
Takeoff and Landing Performance

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Pilot's Handbook of Aeronautical Knowledge

Preface

Acknowledgements

Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making

Appendix

Glossary

Index

The effect of wind on landing distance is large and deserves
proper consideration when predicting landing distance. Since
the aircraft will land at a particular airspeed independent of
the wind, the principal effect of wind on landing distance is
the change in the groundspeed at which the aircraft touches
down. The effect of wind on deceleration during the landing
is identical to the effect on acceleration during the takeoff.

The effect of pressure altitude and ambient temperature is to
define density altitude and its effect on landing performance.
An increase in density altitude increases the landing speed
but does not alter the net retarding force. Thus, the aircraft
at altitude lands at the same IAS as at sea level but, because
of the reduced density, the TAS is greater. Since the aircraft
lands at altitude with the same weight and dynamic pressure,
the drag and braking friction throughout the landing roll have
the same values as at sea level. As long as the condition is
within the capability of the brakes, the net retarding force
is unchanged, and the deceleration is the same as with the
landing at sea level. Since an increase in altitude does not alter
deceleration, the effect of density altitude on landing distance
is due to the greater TAS.

The minimum landing distance at 5,000 feet is 16 percent
greater than the minimum landing distance at sea level. The
approximate increase in landing distance with altitude is
approximately three and one-half percent for each 1,000 feet
of altitude. Proper accounting of density altitude is necessary
to accurately predict landing distance.

The effect of proper landing speed is important when runway
lengths and landing distances are critical. The landing speeds
specified in the AFM/POH are generally the minimum safe
speeds at which the aircraft can be landed. Any attempt to land
at below the specified speed may mean that the aircraft may
stall, be difficult to control, or develop high rates of descent.
On the other hand, an excessive speed at landing may improve
the controllability slightly (especially in crosswinds), but
causes an undesirable increase in landing distance.

A ten percent excess landing speed causes at least a 21 percent
increase in landing distance. The excess speed places a greater
working load on the brakes because of the additional kinetic
energy to be dissipated. Also, the additional speed causes
increased drag and lift in the normal ground attitude, and the
increased lift reduces the normal force on the braking surfaces.
The deceleration during this range of speed immediately after
touchdown may suffer, and it is more probable for a tire to be
blown out from braking at this point.

The most critical conditions of landing performance are
combinations of high gross weight, high density altitude,
and unfavorable wind. These conditions produce the
greatest required landing distances and critical levels of
energy dissipation required of the brakes. In all cases, it is
necessary to make an accurate prediction of minimum landing
distance to compare with the available runway. A polished,
professional landing procedure is necessary because the
landing phase of flight accounts for more pilot-caused aircraft
accidents than any other single phase of flight

In the prediction of minimum landing distance from the AFM/
POH data, the following considerations must be given:
• Pressure altitude and temperature—to define the effect
of density altitude
• Gross weight—which defines the CAS for landing.
• Wind—a large effect due to wind or wind component
along the runway
• Runway slope and condition—relatively small
correction for ordinary values of runway slope, but a
significant effect of snow, ice, or soft ground

A tail wind of ten knots increases the landing distance by
about 21 percent. An increase of landing speed by ten percent
increases the landing distance by 20 percent. Hydroplaning
makes braking ineffective until a decrease of speed to that
determined using Figure 10-17.

For instance, a pilot is downwind for runway 18, and the
tower asks if runway 27 could be accepted. There is a light
rain and the winds are out of the east at ten knots. The pilot
accepts because he or she is approaching the extended
centerline of runway 27. The turn is tight and the pilot must
descend (dive) to get to runway 27. After becoming aligned
with the runway and at 50 feet AGL, the pilot is already 1,000
feet down the 3,500 feet runway. The airspeed is still high by
about ten percent (should be at 70 knots and is at about 80
knots). The wind of ten knots is blowing from behind.

First, the airspeed being high by about ten percent (80 knots
versus 70 knots), as presented in the performance chapter,
results in a 20 percent increase in the landing distance.
In performance planning, the pilot determined that at 70
knots the distance would be 1,600 feet. However, now it
is increased by 20 percent and the required distance is now
1,920 feet.

The newly revised landing distance of 1,920 feet is also
affected by the wind. In looking at Figure 10-18, the affect
of the wind is an additional 20 percent for every ten miles
per hour (mph) in wind. This is computed not on the original
estimate but on the estimate based upon the increased
airspeed. Now the landing distance is increased by another
320 feet for a total requirement of 2,240 feet to land the
airplane after reaching 50 feet AGL.

 

10-16