b. Weekly Check. A field electrician should inspect and service any lights reported as
defective in the daily inspections. The preferred service method is to replace the in pavement
light unit with a spare and take the defective unit back to the shop for repair. The lighting circuit
must be deactivated (fuses pulled) before any maintenance is attempted on the lights. The
following defects may be the cause of the malfunction:
(1) No light
(a) Burned-out Lamp. The lamp may be replaced as described in the
manufacturer's instruction book. The fused disc cutout should also be replaced where used.
(b) Electrical Failure. If the replacement light also fails to operate, or a string
of lights fail, the problem is probably in the series circuit. Troubleshooting procedures are
contained in Section 6.
(2) Dim light
(a) Dirty Light. The exposed optical surface of the in pavement light gets dirty
from exposure to aircraft traffic and weather. The lights should be cleaned periodically as
described in par. 5.5.2.
(b) Light Aiming. Shallow-base in pavement light fixtures sometimes are
twisted out of alignment by aircraft landing or turning. Visually check any dimly burning lights
to see if they are merely misaligned. The alignment procedure is discussed in par. 5.7.2.
(c) Water in the Fixture. Examine the lens for standing water or condensation
behind the lens. If water is present, the fixture should be removed and serviced as described in
c) Monthly Checks. Until a regular maintenance schedule is established, the checks
below should be performed at least once a month; it may be advisable to do them every 2 weeks
at busy facilities. After some experience has been gained, the interval may be adjusted to
(1) Cleaning. Due to their position at ground level, in pavement lights require
frequent cleaning to maintain their specified performance. The frequency with which the lights
must be cleaned depends on the light's location, weather conditions, and number of airport
operations. The lights should be cleaned when the brightness of the fixture is less than 70
percent of the initial brightness when operated at full intensity. A fixture degraded below this is
ineffective for high background brightness and low visibility conditions.
(2) Intensity Checks. To complement the cleaning process, a check should be
made of the light output of several fixtures located on different parts of the field, particularly
near the ends of the field and in the touchdown zone. The light output may be measured with a
photographic 1 degree spotmeter as explained in par. 5.7.2.g). The procedure may be conducted
to provide the following information:
(a) Before cleaning, to establish whether cleaning is necessary, or
(b) After cleaning, to check the effectiveness of the cleaning and determine the
degradation of the internal optical assembly. Lights that are below minimum levels should be
scheduled for removal and servicing.