Page 113 - Planning and Design of Airports

Air craft Characteristics Related to Airport Design 83

Thus, in the discussion which follows, the terms runway and full-
strength pavement are synonymous. In any discussion of the effect of
the regulations on the length of the runway, however, it is important
to note that the current regulations for turbine-powered aircraft do
not require a runway for the entire takeoff distance, while the regula-
tions for piston-engine aircraft normally do.
To indicate why there is a difference in the two regulations with
regard to the length of full-strength pavement, it is necessary to exam-
ine in more detail the regulations pertaining to turbine-powered
transports.
These three criteria as defined by the current turbine-powered
transport regulations, FAR Part 25 [12] and Part 121 [23], are illustrated
in Fig. 2-9.
Figure 2-9a illustrates the required landing distance. The regula-
tions state that the landing distance (LD) required for an aircraft land-
ing on a given runway must be sufficient to permit the aircraft to
come to a full stop, stop distance (SD), within 60 percent of this dis-
tance, assuming that the pilot makes an approach at the proper speed
and crosses the threshold of the runway at a height of 50 ft. The land-
ing distance must be of full-strength pavement. The landing distance
for piston-engine aircraft is defined in exactly the same manner.
Figure 2-9c, illustrates the runway length requirements for a
normal takeoff with all engines fully operating, Fig. 2-9c defines a
takeoff distance (TOD), which, for a specific weight of aircraft, must
be 115 percent of the actual distance the aircraft uses to reach a height
of 35 ft (D35). Not all of this distance has to be of full-strength pave-
ment. What is necessary is that all this distance be free from obstruc-
tions to protect against an overshooting takeoff. Consequently the
regulations permit the use of a clearway (CL) for part of this distance.
A clearway is defined as a rectangular area beyond the runway not
less than 500 ft wide and not longer than 1000 ft in length, centrally
located about the extended centerline of the runway, and under the
control of the airport authorities. The clearway is expressed in terms
of a clearway plane, extending from the end of the runway with an
upward slope not exceeding 1.25 percent above which no object nor
any portion of the terrain protrudes, except that threshold lights may
protrude above the plane if their height above the end of the runway
is not greater than 26 in and if they are located to each side of the
runway. Up to one-half the difference between 115 percent of the dis-
tance to reach the point of liftoff, liftoff distance (LOD), and the takeoff
distance may be clearway. The remainder of the takeoff distance must
be full-strength pavement and is identified as the takeoff run (TOR).
Figure 2-9b illustrates the engine-failure case, described as the
case where one engine fails at a critical point during an aircraft takeoff
roll, and the pilot makes an immediate judgmental decision whether
or not to continue with a takeoff, or perform an emergency stop.