Page 243 - Planning and Design of Airports

Geometric Design of the Airfield 207

parallel runways for simultaneous instrument approaches. However,
there is evidence that these distances are conservative and steps are
being taken to reduce it. The ultimate goal is to reduce this distance
by about one-half. For dependent instrument approaches both the
FAA and ICAO recommend centerline separations of 3000 ft (915 m).
For triple and quadruple simultaneous instrument approaches, the
FAA requires 5000-ft separation between runway centerlines,
although will allow 4300 ft separations on a case-by-case basis.
Both the FAA and ICAO specify that two parallel runways may
be used simultaneously for radar departures in IMC if the centerlines
are separated by at least 2500 ft (760 m). The FAA requires a 3500-ft
centerline separation for simultaneous nonradar departures. If two
parallel runways are to be operated independently of each other in
IMC under radar control, one for arrivals and the other for depar-
tures, both the FAA and ICAO specify that the minimum separation
between the centerlines is 2500 ft (760 m) when the thresholds are
even. If the thresholds are staggered, the runways can be brought
closer together or must be separated farther depending on the amount
of the stagger and which runways are used for arrivals and depar-
tures. If approaches are to the nearest runway, then the spacing may
be reduced by 100 ft (30 m) for each 500 ft (150 m) of stagger down to
a minimum of 1200 ft (360 m) for airplane design groups V and VI
and 1000 ft (300 m) for all other aircraft. However, if the approaches
are to the farthest runway, then the runway spacing must be increased
by 100 ft (30 m) for each 500 ft (150 m) of stagger.
Sight Distance and Longitudinal Profile
The FAA requirement for sight distance on individual runways
requires that the runway profile permit any two points 5 ft above the
runway centerline to be mutually visible for the entire runway length.
If, however, the runway has a full length parallel taxiway, the runway
profile may be such that an unobstructed line of sight will exist from
any point 5 ft above the runway centerline to any other point 5 ft
above the runway centerline for one-half the runway length.
The FAA recommends a clear line of sight between the ends of
intersecting runways. The terrain must be graded and permanent
objects designed and sited so that there will be an unobstructed
line of sight from any point 5 ft above one runway centerline to
any point 5 ft above an intersecting runway centerline within the
runway visibility zone. The runway visibility zone is the area
formed by imaginary lines connecting the visibility points of the
two intersecting runways. The runway visibility zone for inter-
secting runways is shown in Fig. 6-21. The visibility points are
defined as follows:
1. If the distance from the intersection of the two runway cen-
terlines is 750 ft or less, the visibility point is on the centerline
at the runway end designated by point a in Fig. 6-21.