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 MIL-HDBK-1023/4
b) Monthly checks
(1) Record the input and output voltages of the control cabinet and compare with
previous readings to ascertain the rate of deterioration of the system.
(2) Clear vegetation or obstructions from the front of all lights to ensure adequate
visibility. Diesel fuel or other approved chemicals can be used to help control the growth of
vegetation around the lights.
c) Semiannual checks
(1) Check light fixtures for alignment. The elevation angle settings of the lamps
differ at each light bar station. These angles should be permanently displayed at each station to
facilitate maintenance.
(2) Check structures carefully for hidden corrosion. Special attention should be
paid to wood-to-wood, wood-to-steel, wood-to-earth, and steel-to-earth contacts.
(3) Check the approach area for new structures or for growth of vegetation which
may violate the approach clearance criteria. A clear line-of-sight is required from any point on a
plane 1/2 degree below the glide slope extending 250 feet (75 m) from each side of centerline for
a distance up to 1,600 feet (500 m) in advance of the outermost lights in the system. If objects
block a view of the lights and cannot be removed, refer the problem to appropriate airport
authorities.
(4) If used, check and adjust the photoelectric controls. Use a photometer to verify
the photoelectric control is adjusted to turn the lights on at a north-sky light intensity level of 35
footcandles and turn off at 58 footcandles. If the unit is properly adjusted, the system will
operate on the high brightness position on a relatively clear day from approximately 1/2 hour
before sunset to 1/2 hour after sunrise. Also, check the orientation of the photoelectric cell. The
cell should be oriented by aiming at the north sky at or slightly above the northern horizon. If
adjustments are required, refer to the applicable manufacturer's instruction book for detailed
adjustment procedures.
d) Annual checks
(1) Check pole-top-mounted or termination switches.
(2) Check all main power and control cable insulation resistance (refer to par. 4.7).
Record reading on the insulation resistance form. Compare the current reading with previous
readings to determine if cables are deteriorating.
(3) Check fuse holders, breakers, and contacts. Contacts in the control cabinet
should be carefully inspected. If the contacts are badly worn, they should be replaced. Do not
file or burnish contacts. Discoloration of contacts or some roughness due to normal arcing is not
harmful. The contacts should be wiped to remove the dust. Blown fuses should be replaced with
the correct size and type. Do not assume that the old fuse is the correct size and type.
f) Unscheduled Maintenance. Consideration should be given to group changing of all
PAR 38, 150-watt lamps after 1800 hours of operation on maximum brightness, recorded on an
elapsed time meter.
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