Page 344 - Planning and Design of Airports

302 Airp o r t D e sign

Far Bar
= Red
Near Bar = White

Below Glide Path On Glide Path Above Glide Path
FIGURE 8-6 Two bar VASI system (FAA/AIM ).

the downwind bar and the third bar is the upwind bar. In other words,
pilots of large wide bodied aircraft ignore the bar closest to the run-
way threshold and use the other two bars for visual reference. The
location of the lights for VASI-6 systems is shown in Fig. 8-7.
The more common systems in use in the United States are the
VASI-2, VASI-4, VASI-12, and VASI-16. VASI systems are particularly
useful on runways that do not have an instrument landing system or
for aircraft not equipped to use an instrument landing system.

Precision Approach Path Indicator
The FAA presently prefers the use of another type of visual approach
indicator called the precision approach path indicator (PAPI) [20]. This
system gives more precise indications to the pilot of the approach
path of the aircraft and utilizes only one bar as opposed to the mini-
mum of two required by the VASI system. A schematic diagram of the
PAPI system is shown in Fig. 8-8.
The system consists of a unit with four lights on either side of the
approach runway. By utilizing the color scheme indicated on Fig. 8-8,
the pilot is able to ascertain five approach angles relative to the proper
glide slope as compared with three with the VASI system. One of the
problems with the VASI system has been the lack of an immediate
transition from one color indication to another resulting in shades of
colors. The PAPI system resolves this problem by providing an instant
transition from one color indication to another as a reaction to the

Far Bar

Middle Bar
Near Bar

Below Both On Lower On Upper Above Both
Glide Paths Glide Path Glide Path Glide Paths
FIGURE 8-7 Three bar VASI-6 system.