Quantcast Preventive Maintenance Inspection (PMI) Procedures

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MIL-HDBK-1023/4
(7) Glassware. Clean and polish all glassware, both inside and outside, using a
type of non-abrasive cleaner that will not scratch the lens.
c) Semiannual checks
(1) Input Voltage. Check the input voltage and record the reading. It should be
within 5 percent of the rated lamp voltage. Voltage levels higher than a lamp's nominal rating
will prematurely reduce the lamp's life proportionally to the increased voltage, and conversely,
voltage levels lower than a lamp's nominal rating will reduce the lamp's light output
proportionally to the reduced voltage. The measurement should be made at the beacon lamp
terminals, with all field equipment energized, so the voltage reading will reflect operating
conditions. Beacon lamps are very sensitive to voltage changes. A drop of 10 percent will
reduce the light output 31 percent while a rise of 10 percent will shorten the lamp life 72 percent.
Voltage regulation on airport power service is often quite poor, and frequently power supply
conditions change so that the existing voltage is different from that measured at the time of
installation. This is one of the most common causes of short-lived beacon lamps, and it is,
therefore, important that the voltage ratings of the lamps used correspond closely to the actual
prevailing supply voltage. If the voltage is out of tolerance, contact the power company to
correct the situation, or install a compensating device such as an autotransformer.
(2) Lamp Focus and Beam Elevation. Verify that beacon beam is narrow, well
defined, and projects horizontally. If beam elevation is dispersed and/or projects other than
horizontally, focus and beam elevation should be adjusted.
(3) Lubrication
(a) Vertical Main Shaft. Beacons supplied with a grease-gun fitting should be
lubricated twice a year under ordinary operation. Use a high-quality, low-temperature silicone
grease (ESSO #325 or equivalent).
(b) Motor. If the motor is supplied with oil cups, lubricate with SAE 20 oil. If
there are no oil cups, the bearings are sealed and do not need servicing.
(c) Ring Gear. Apply a small amount of grease (ESSO #325 or equivalent) to
the ring gear.
CAUTION:
Using an excessive amount of grease will result in its dropping down upon the
slip rings and causing poor contact and arcing.
(d) Padlocks. Any padlocks should be lubricated with dry graphite powder or
equivalent.
(4) Switches. Check the operation of electrical switchblades and clips for good
contact. Switches should have tension between the blades and hinges, but must also be free to
move. Loose-fitting hinges or clips will cause overheating and deterioration of the switch parts.
Severe overheating can usually be detected by a bluish color of the switch part affected.
(5) Lightning Protection System. Check the lightning rod connections for
tightness, and check the condition of the down conductor for corrosion or damage. Check and
record the ground resistance. Compare the reading with the previous ground resistance checks.
Reading must be less than 25 ohms. If the reading exceeds 25 ohms, immediate action must be
taken to correct the grounding problem.
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