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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



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




Takeoff obstacle clearance.
Figure 10-37. Takeoff obstacle clearance.

First Segment
This segment is included in the takeoff runway required
charts, and is measured from the point at which the aircraft
becomes airborne until it reaches the 35-foot height at the
end of the runway distance required. Speed initially is VLO
and must be V2 at the 35 foot height.

Second Segment
This is the most critical segment of the profile The second
segment is the climb from the 35 foot height to 400 feet
above the ground. The climb is done at full takeoff power
on the operating engine(s), at V2 speed, and with the flaps
in the takeoff configuration. The required climb gradient
in this segment is 2.4 percent for two-engine aircraft, 2.7
percent for three-engine aircraft, and 3.0 percent for four engine

Third or Acceleration Segment
During this segment, the airplane is considered to be
maintaining the 400 feet above the ground and accelerating
from the V2 speed to the VFS speed before the climb profile
is continued. The flaps are raised at the beginning of the
acceleration segment and power is maintained at the takeoff
setting as long as possible (5 minutes maximum).

Fourth or Final Segment
This segment is from the 400 to 1,500 foot AGL altitude
with power set at maximum continuous. The required climb
in this segment is a gradient of 1.2 percent for two-engine
airplanes, 1.55 for three-engine airplanes, and 1.7 percent
for four-engine airplanes.

Second Segment Climb Limitations
The second segment climb requirements, from 35 to 400
feet, are the most restrictive (or hardest to meet) of the
climb segments. The pilot must determine that the second
segment climb is met for each takeoff. In order to achieve this
performance at the higher density altitude conditions, it may
be necessary to limit the takeoff weight of the aircraft.

It must be realized that, regardless of the actual available
length of the takeoff runway, takeoff weight must be
adjusted so that the second segment climb requirements can
be met. The aircraft may well be capable of lifting off with
one engine inoperative, but it must then be able to climb
and clear obstacles. Although second segment climb may
not present much of a problem at the lower altitudes, at the
higher altitude airports and higher temperatures, the second
segment climb chart should be consulted to determine the
effects on maximum takeoff weights before figuring takeoff
runway distance required.

Air Carrier Obstacle Clearance Requirements

Regulations require that large transport category turbine
powered aircraft certificated after September 30, 1958, be
taken off at a weight that allows a net takeoff flightpath
(one engine inoperative) that clears all obstacles either by
a height of at least 35 feet vertically, or by at least 200 feet
horizontally within the airport boundaries and by at least 300
feet horizontally after passing the boundaries. The takeoff
flightpath is considered to begin 35 feet above the takeoff
surface at the end of the takeoff distance, and extends to a
point in the takeoff at which the aircraft is 1,500 feet above
the takeoff surface, or at which the transition from the takeoff
to the en route configuration is completed. The net takeoff
flightpath is the actual takeoff flightpath reduced at each point
by 0.8 percent for two engine aircraft, 0.9 percent for three engine
aircraft, and 1.0 percent for four-engine aircraft.

Air carrier pilots therefore are responsible not only for
determining that there is enough runway available for an
engine inoperative takeoff (balanced field length), and
the ability to meet required climb gradients; but they must
also assure that the aircraft will safely be able to clear any
obstacles that may be in the takeoff flightpath The net
takeoff flightpath and obstacle clearance required are shown
in Figure 10-37.