UFC 3-535-01
17 November 2005
The aiming angle for the PAPI glide path must not be less than 1.2 degrees above the
PAPI clearance plane. A plan view of the PAPI clearance plane is a triangle which
begins at a point on the runway centerline 90 meters (300 feet) downwind from the
PAPI RRP and diverges outward into the approach at 10 degrees on either side of the
extended runway centerline for a distance of 6.44 kilometers (4 statue miles) from the
threshold. (See Figure 3-14.) Where the sides of the plane do not encompass the
runway width at the threshold, the width at that point must be increased to the runway
width while maintaining the 10 degree angle of divergence.
3-7.5
Power Requirements
Provide the electrical power for the PAPI system from a separate 120/240 volt circuit or
a 6.6A series circuit. The 120/240 volt circuit is for parallel operation with control by
photocell and selector switch at the unit. Energize the 6.6A series circuit by a constant-
current regulator. A 4 kW constant current regulator, three or five intensity steps, is used
to energize the PAPI on a series circuit. The number of brightness steps should match
that of the runway edge lighting system. When the PAPI is required to be on a series
circuit, the lights must be connected to the series circuit by series isolation transformers
of suitable capacity for each lamp. Emergency power is not essential but should be
used if available. The emergency transfer of power should be the same as the runway
edge lights. Monitoring of the PAPI is not required except for daily visual checks of
operations and periodic checks for proper aiming.
3-7.6
Control Requirements
Control the PAPI on/off manually from the air traffic control tower and from the airfield
lighting vault. Brightness control will be manual, however, it may also be controlled by
photocell or pilot radio control at airfields without air traffic controllers, or where the air
traffic control tower is not manned full time. At these locations, provide an electrical
interlock between the PAPI and the runway edge lights. This interlock may be an
electrical contactor or radio interface unit to ensure that, during the hours of darkness
the PAPI is only on when the runway edge lights are on. During hours of daylight, the
PAPI will be capable of operating independently of the runway edge lights. PAPI on/off
and intensity controls must be included on the airfield lighting control panel.
3-7.6.1
Provide radio control when required by using an FAA L-854 radio
controller (see FAA AC 150/5345-49, Specification L-854, Radio Control Equipment),
which allows the PAPI to be turned on by a pilot on approach or by a ground control
station. Three clicks must provide for step 2 on a 3-step system and step 3 on a 5-step
system (middle brightness step), while 5 clicks must provide for the PAPI to match the
runway edge lighting brightness step at step 2 and higher. The photocell provides full
intensity during daylight.
3-7.6.2
The photocell must provide for full intensity of the PAPI (highest
brightness step) when the ambient lighting reaches 50-60 footcandles, and reduced
brightness when the ambient lighting decreases to 25-30 footcandles (step 2 for a 3-
step regulator, and step 3 for a 5-step regulator). The photoelectric control should have
a time delay of at least 30 seconds to prevent false switching from stray light or
temporary shadows. The photocell should be installed at an unobstructed location to
aim towards the north horizon.
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