Page 340 - Planning and Design of Airports

298 Airp o r t D e sign

sequenced flashing lights (ALSF-1), and three medium-intensity ALSs
(MALSR, MALS, MALSF).
In each of these systems there is a long transverse crossbar located
1000 ft from the runway threshold to indicate the distance from the
runway threshold. In these systems roll guidance is provided by
crossbars of white light 14 ft in length, placed at either 100- or 200-ft
centers on the extended runway centerline. The 14-ft crossbars consist
of closely spaced five-bulb white lights to give the effect of a continuous
bar of light.
The high-intensity ALS is 2400 ft long (some are 3000 ft long) with
various patterns of light located symmetrically about the extended
runway centerline and a series of sequenced high-intensity flashing
lights located every 100 ft on the extended runway centerline for the
outermost 1400 ft. In the high-intensity ALSs the 14-ft crossbars of
five-bulb white light are placed at 100-ft intervals and in the medium-
intensity ALSs these crossbars of white light are placed at 200-ft inter-
vals both for a distance of 2400 ft from the runway threshold on the
extended runway centerline. The high-intensity ALSs have a long
crossbar of green lights at the edge of the runway threshold. The
ALSF-2 system, shown in Fig. 8-5a, has two additional crossbars con-
sisting of three-bulb white light crossbars which are placed symmetri-
cally about the runway centerline at a distance of 500 ft from the runway
threshold and two additional three-bulb red light crossbars are placed
symmetrically about the extended runway centerline at 100-ft inter-
vals for the inner 1000 ft to delineate the edges of the runway surface.
The ALSF-1 system, shown in Fig. 8-5b, has two additional crossbars
consisting of five-bulb red light crossbars which are placed symmetri-
cally about the runway centerline at a distance of 100 ft from the run-
way threshold to delineate the edge of the runway and two additional
three-bulb red light crossbars placed symmetrically about the extended
runway centerline at 200 ft from the runway threshold.
The MALSR system, shown in Fig. 8-5c, is a 2400-ft medium-
intensity ALS with runway alignment indicator lights (RAILs). The
inner 1000 ft of the MALSR is the MALS portion of the system and the
outer 1400 ft is the RAIL portion of the system. The system has
sequential flashing lights for the outer 1000 ft of the system. It is rec-
ommended for category I precision approaches. The simplified short
approach lighting system (SSALR) has the same configuration as the
MALSR system.
At smaller airports where precision approaches are not required,
a medium ALS with sequential flashers (MALSF) or with sequenced
flashers (MALS) is adequate. The system is only 1400 ft long com-
pared to a length of 2400 ft for a precision approach system. It is
therefore much more economical, an important factor at small air-
ports. The MALSF, similar to the MALSR shown in Fig. 8-5d, is a short
approach medium-intensity ALS but the sequenced flashers replace