Page 112 - Planning and Design of Airports

82 Airp o r t Pl anning

would range from 110 to 140 mi/h or more. The landing speeds are in
the same range. Therefore hydroplaning can be a hazard to jet opera-
tions. Hydroplaning can develop when the depth of water or slush is
on the order of 0.2 in or less, the exact depth depending on tire tread
design, condition of the tires, and the texture of the pavement sur-
face. Smooth tread operating on a smooth pavement surface requires
the least depth of fluid for hydroplaning.
To reduce the hazard of hydroplaning and to improve the coeffi-
cient of braking friction, runway pavements have been grooved in a
transverse direction. The grooves form reservoirs for the water on the
surface. The FAA is conducting extensive research to establish stand-
ards for groove dimensions and shape [54]. In the past the grooves
were normally ¼ in wide and deep and spaced 1 in apart [44].

Declared Distances
Transport category aircraft are licensed and operated under the code
of regulations known as the Federal Aviation Regulations (FAR). This
code is promulgated by the federal government in coordination with
industry. The regulations govern the aircraft gross weights at takeoff
and landing by specifying performance requirements, known as
declared distances which must be met in terms related to the runway
lengths available. The regulations pertaining to turbine aircraft con-
sider three general cases in establishing the length of a runway neces-
sary for safe operations. These three cases are

1. A normal takeoff where all engines are available and suffi-
cient runway is required to accommodate variations in liftoff
techniques and the distinctive performance characteristics of
these aircraft
2. Takeoff involving an engine failure, where sufficient runway
is required to allow aircraft to continue the takeoff despite the
loss of power, or else brake to a stop
3. Landing, where sufficient runway is required to allow for
normal variation in landing technique, overshoots, poor
approaches, and the like

The regulations pertaining to piston-engine aircraft retain in prin-
cipal the above criteria, but the first criterion is not used. This particu-
lar regulation is aimed toward the everyday, normal takeoff maneuver,
since engine failure occurs rather infrequently with turbine-powered
aircraft. The runway length needed at an airport by a particular type
and weight of turbine-powered aircraft is established by one of the
foregoing three cases, whichever yields the longest length.
In the regulations for both piston-engine aircraft and turbine-
powered aircraft, the word runway refers to full-strength pavement (FS).