Page 116 - Planning and Design of Airports

Air craft Characteristics Related to Airport Design 85

Federal regulations specify that the takeoff distance required dur-
ing the engine-failure case is the actual distance to reach a height of
35 ft (D35) with no percentage applied as in the all-engine takeoff
case. This recognizes the infrequency of occurrence of engine failure.
The regulations again permit the use of a clearway, in this case up to
one-half the difference between the liftoff distance and the takeoff
distance, the remainder being full-strength pavement. The regula-
tions for piston-engine aircraft normally require full-strength pave-
ment for the entire takeoff distance.
The engine-failure case also requires that sufficient distance must
also be available to stop the airplane rather than continue the takeoff.
The speed at which engine failure is assumed to occur is selected by
the aircraft manufacturer and is referred to as the critical engine-failure
speed or decision speed, V . If the engine fails at a speed greater than
1
this speed, the pilot has no choice but to continue the takeoff. If an
engine actually fails at or prior to this selected speed, the pilot brakes
to a stop. This distance required, from beginning of the takeoff roll to
the emergency stop is referred to as the accelerate-stop distance (DAS).
For piston-engine aircraft only full-strength pavement is normally
used for this purpose. The regulations for turbine-powered aircraft,
however, recognize that an aborted takeoff is relatively rare and per-
mit use of lesser strength pavement, known as stopway (SW), for that
part of the accelerate-stop distance beyond the takeoff run. The stop-
way is defined as an area beyond the runway, not less in width than
the width of the runway, centrally located about the extended center-
line of the runway, and designated by the airport authorities for use
in decelerating the aircraft during an aborted takeoff. To be consid-
ered as such, the stopway must be capable of supporting the airplane
during an aborted takeoff without inducing structural damage to the
aircraft. Engineered material arresting systems (EMAS) are being
used as for this purpose with increasing frequency.
Based on the above requirements, aircraft operators estimate a
required field length (FL) for each operation. The field length is gener-
ally made up of three components, namely, the full-strength pave-
ment (FS), the partial strength pavement or stopway (SW), and the
clearway (CL).
The preceding regulations for turbine-powered aircraft may be
summarized for each of the cases in equation form to find the required
field length.
Normal takeoff case:

FL = FS + CL (2-7)
1 1 1max
where
TOD = 1.15(D35 ) (2-7a)
1 1
CL = 0.50[TOD − 1.15(LOD )] (2-7b)
1max 1 1