Tower Control Unit
The control switch on the tower control unit works
only when the local/remote control unit in the timer
cabinet is in the REMOTE position. The audible and
visible monitoring alarms, however, are operable
whenever the system is in use, even if the local/remote
unit is at the LOCAL-ON position. Adjustments are
provided on the panel for regulating the brightness of
the two green monitor lights and the loudness of the
buzzer. A push-button switch is used to test the
operation of the buzzer.
MAINTENANCE OF AIRFIELD
Regardless of the design of an airfield system,
maintenance is highly recommended to ensure the
operational dependency of the field. Routine
scheduled downtime is much better than unscheduled
downtime in the midst of an operation. Simple visual
inspection plus periodic resistance readings of circuit
devices, components, and cables reveal probable
Do not get caught in the jury-rigged trap. This
tendency to patch, bypass, piece together, or otherwise
rig a system to work just for a little while can be as
dangerous as a coiled rattlesnake. That temporary
fix is just sitting there waiting to catch some
uninformed individual sent out to work on the system.
This section covers routine maintenance for airfield
lighting and underground systems, troubleshooting
cable systems, and cable splicing and repair.
Routine maintenance includes, but is not limited
to, cleaning, adjusting, lubricating, painting, and
treating for corrosion. Components and connections
must be checked for condition and security. The
insulation of the conductors should be checked for
good condition and burns, scrapes, breaks, cracks, or
evidence of overheating.
During your visual inspection of an airfield
lighting wiring system, you should check the constant-
current regulator (CCR) for chipped or cracked
porcelain bushings, correct connections, proper fuses
and switches, and relays for freedom of movement.
Only relay panel covers should be removed. It is not
necessary to open the main regulator tank. All covers
that are removed should be cleaned and then
reinstalled tightly. Cable and isolation transformer
connectors require close visual inspections for cuts,
bruises, or other mishandling; these conditions could
cause premature failure to the system. The mating
surfaces of these molded rubber connectors must be
clean and dry when they are plugged together. Either
dirt or moisture prevents the mating surfaces from
making complete surface contact and causes a failure
at the connector. When connectors are plugged
together, trapped air can cause them to disengage
partially. Wait a few seconds and push them together
again. Apply two or three turns of tape to hold them in
place. When the connectors are clean, dry, and taped
properly, the connection is equal or superior to a high-
Check light fixture connections for tightness.
Look for cable bends that are too sharp; sharp bends
can cause insulation breakdown or connector failure.
Once all components of the system have been
visually inspected for damage and the cable system has
been checked with a megger and hi-pot, make an
operational check ofthe entire airfield lighting system.
1. Working from the control tower with an
observer in the vault, operate each switch of the airport
and taxiway panel, so that each position is reached at
least twice. You must have radio or telephone
communication with the observer in the vault during
this operation. The observer in the vault determines that
each switch properly controls its corresponding circuit.
2. Repeat this operation from the vault (alternate
control panel) in the same manner, assuring that each
switch position is reached twice.
3. Now, repeat the test by using the local control
switches on the regulator.
4. Operate each lighting circuit at maximum
brightness for 6 continuous hours. Make a visual
inspection of all lights, both at the beginning and at the
end of this test to assure that the proper number of lights
are operating at full brightness. Measure lamp terminal
voltage on at least one lamp in each multiple circuit to
assure that this voltage is within ±5 of the rated lamp
voltage. Dimming of some or all of the lights in a circuit
indicates grounded cables.