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 LIGHTING SYSTEMS

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 trouble areas.

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

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.

Visual Inspection

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 IT 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 moldedrubber 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 partially disengage. 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 properly taped, the connection is equal or superior to a high-voltage splice.

Check light fixture connections and counterpoise connections for tightness. Look for cable bends that are too sharp; sharp bends can cause insulation breakdown or connector failure.

Operational Check

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 of the 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.

Condenser Discharge Light System

Periodic maintenance of this system is fairly simple. Remember, however, that high voltages exist in the components of the system and you must be extra careful. One such area is the flash capacitor. This capacitor may contain as much as 2,000 volts. Anyone working on the light fixture should make sure that this capacitor is discharged before working on the light unit. The capacitor should bleed down through its resistor network in 5 seconds; however, the capacitor should be shorted out before any work being done inside the unit. In a flush unit, short between terminals 7 and 10 of the terminal board with a shorting stick. In the elevated light, short the two contacts on the left side of the flashtube socket.

This must be done before any work is done inside the light unit, such as changing a flashtube or cleaning the reflector.

Since these are sealed units, cleaning the reflectors should rarely be required. When such cleaning is required, be sure to use a nonabrasive cleaner. The lenses in both the elevated and flush units should be cleaned periodically, depending on the local conditions.

Inspect the timer contacts to see that they are clean and making good contact. If not, the stationary timer contacts can be adjusted. The timer gears of the master sequence timer require periodic lubrication. Match the grease to the ambient temperatures expected in your particular area. NEVER use a graphite-based grease, as graphite is electrically conductive.

Check to see that both pairs of green indicator lights will light. When only one lamp is lit on either unit, the other bulb has burned out. To replace one of these bulbs, remove the front panel, pull off the colored lens, push out the old bulb, and insert the new bulb from the front of the panel. Replace the lens and panel.