(3) Since there are variations in the manufacture and installation of in pavement
lights, some lights may remain below the standard value, as measured in step (1) above, even
after cleaning and servicing. If the difference in light output is significant, then it may be
necessary to establish individual standards for lights with sub-par readings.
Precision Approach Path Indicator System (PAPI/CHAPI)
Preventive Maintenance Inspection Procedures. A typical layout of the PAPI system is
shown in Figure 15. To perform the PMIs contained in Table 14, proceed as follows; for
tolerances see Appendix A, Table A-5.
a) Daily Checks. Confirm all lamps are burning and are of equal brightness.
Adequate spare lamps should be available to permit a complete replacement of all lamps in the
system. Spare bypass fuses, if used, should also be stocked. Lamps should be replaced
immediately if they burn out or become darkened. If the PAPI uses bypass fuses, never replace a
lamp until the associated fuse is checked.
b) Monthly checks
(1) Check operation of controls. Check photocell brightness control and runway
light circuit interlock (if used), radio control (if used), and/or remote control switch.
(2) Check for damage by mowers, snowplows, etc.
(3) Clean lamps and filters.
(4) Visually check mechanical parts for cleanliness, burned wires or connections,
cracked insulators, lamps or filters, etc.
(5) Check if the lightning arresters and/or surge suppressers are scorched or show
other signs of being burned out, and replace as necessary. Also, check after electrical storms.
(6) Check in the lamp boxes and adapter units for damage or debris from water,
mice, wasps, bird nests, spider webs, etc., and clean or repair as needed.
(7) Check for burrows or other signs of rodent activity in vicinity of cables; take
steps to discourage their presence to minimize likelihood of cable damage.
(8) If an adapter unit is used, read and record the output current and the input
voltage to the adapter unit.
(9) Check the horizontal and lateral alignment of the light boxes, and check the
aiming (vertical angle) with the PAPI aiming instrument. Record the angle setting and the date
in a maintenance log. It is particularly important to check aiming frequently whenever the soil
freezes or thaws or has a change in moisture content (especially clay soils).
(10) Check leveling and operating of tilt switch - if applicable.
c) Quarterly Checks. Check the obstacle-free approach plane for clearance from tree
growth, new towers, pole lines, or other obstacles. The obstacle free plane is 4 miles long and
extends 10 degrees on either side of the runway centerline.