Ahh Yes The Old Relay Quandry!!!!

Those of you who work the Line know what the picture to the right is. For the rest of you, it is a picture of a bunch of relays that live behind the First Officers seat up in the Flight Deck on the 737. Out working the Line you may get calls like "the so and so light is on and it won't shut off" or "I switched power and the Master caution light won't turn on". All of these are real problems to our end users (Pilots) but often not "real" problems in a sense.

I will explain it like this, the 737 must have hundreds if not thousands of relays in it. For any one who does not know what a relay is an electrically operated switch. In other words electricity is supplied to the relay and a switch or contact is made to initiate the flow of electricity to operate a system. Relays are wonderful little and big things that allow the plane to turn on an or off systems very quickly and often times without Pilot or Mechanic actions. Relays must make or break systems thousands of times a flight.

As with any mechanical thing relays some times "hang up" as we say. When a relay hangs up it stays on or off when the power to the coil (the coil opens and or closes the switch) is off. As you can imagine when a relay hangs up it causes erroneous indications or effects on the Flight Deck.

More often than not you can reset a hung relay by simply switching power sources. In other words switch from Ground Power to APU Power and back again. The interruption of power can relax the relay and the system goes back to normal, you look like a hero! There are times, however when that will not work. The next step is not in the Maintenance Manual but it is a time proven technique. Take your flip-flop screwdriver and give the relay a little love tap. This is probably the most used technique out there. If the system or light goes back to normal you have figured it out! There are of course times when nothing but changing the relay will work but, take a look at the picture above and try to figure out which relay is giving you the problem. A look at a wiring diagram will tell you the relay to look for if you are lucky but often there are two, three, four or more relays in a system. Now is the time to take off your High Tech Mechanix Gloves and feel for the HOT relay. Relays that get stuck get hot, quickly!

Changing out the relay is easy enough when you are at the home base with Stores available. But my question is: What to do when you are down line on a road trip and have no relay, no stores, and the next part can not get to you for four or five hours? If the old love tap worked and there are no other problems how do you sign it off? Sure arrangements can be made to have the relay changed downline or at the RON if it is in a maintenance station but, how far should you take it? My personal feeling is if there are no other problems, if you can not get the issue to repeat again, if the plane is going one or at the most two legs and then to maintenance, if the Flight Crew is comfortable with it, than it can be signed off as "Reset system" or "System operates as normal".

What do you think? It's kind of a sticky one, huh?