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Pilot's Handbook of Aeronautical Knowledge
Aircraft Performance
Air Carrier Obstacle Clearance Requirements

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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 usual method of computing net takeoff flightpath
performance is to add up the total ground distances required
for each of the climb segments and/or use obstacle clearance
performance charts in the AFM. Although this obstacle
clearance requirement is seldom a limitation at the normally
used airports, it is quite often an important consideration
under critical conditions such as high takeoff weight and/or
high density altitude. Consider that at a 2.4 percent climb
gradient (2.4 feet up for every 100 feet forward) a 1,500
foot altitude gain would take a horizontal distance of 10.4
NM to achieve.

Summary of Takeoff Requirements
In order to establish the allowable takeoff weight for a
transport category aircraft, at any airfield, the following must
be considered:
• Airfield pressure altitude
• Temperature
• Headwind component
• Runway length
• Runway gradient or slope
• Obstacles in the flightpath

Once the above details are known and applied to the
appropriate performance charts, it is possible to determine
the maximum allowable takeoff weight. This weight would
be the lower of the maximum weights as allowed by:
• Balanced field length required
• Engine inoperative climb ability (second segment
limited)
• Obstacle clearance requirement

In practice, restrictions to takeoff weight at low altitude
airports are usually due to runway length limitations; engine
inoperative climb limitations are most common at the higher
altitude airports. All limitations to weight must be observed.
Since the combined weight of fuel and payload in the aircraft
may amount to nearly half the maximum takeoff weight,
it is usually possible to reduce fuel weight to meet takeoff
limitations. If this is done, however, flight planning must be
recalculated in light of reduced fuel and range.

Landing Performance
As in the takeoff planning, certain speeds must be considered
during landing. These speeds are shown below.
• Vvo—stalling speed or the minimum steady flight
speed in the landing configuration.
• Vref—1.3 times the stalling speed in the landing
configuration. This is the required speed at the 50-foot
height above the threshold end of the runway.
• Approach climb—the speed which gives the best climb
performance in the approach configuration, with one
engine inoperative, and with maximum takeoff power
on the operating engine(s). The required gradient of
climb in this configuration is 2.1 percent for two engine
aircraft, 2.4 percent for three-emgine aircraft,
and 2.7 percent for four-engine aircraft.
• Landing climb—the speed giving the best performance
in the full landing configuration with maximum
takeoff power on all engines. The gradient of climb
required in this configuration is 3.2 percent.

Planning the Landing
As in the takeoff, the landing speeds shown above should be
precomputed and visible to both pilots prior to the landing.
The Vref speed, or threshold speed, is used as a reference
speed throughout the traffic pattern or instrument approach
as in the following example:
Vref plus 30K D o w n w i n d o r p r o c e d u r e t u r n
Vref plus 20K Base leg or final course inbound to final
fix
Vref plus 10K Final or final course inbound from .x
(ILS final)
Vref Speed at the 50 foot height above the
threshold

Landing Requirements
The maximum landing weight of an aircraft can be restricted
by either the approach climb requirements or by the landing
runway available.

Approach Climb Requirements
The approach climb is usually more limiting (or more difficult
to meet) than the landing climb, primarily because it is based
upon the ability to execute a missed approach with one engine
inoperative. The required climb gradient can be affected
by pressure altitude and temperature and, as in the second
segment climb in the takeoff, aircraft weight must be limited
as needed in order to comply with this climb requirement.

 

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