March 1, 1999
It's been very quiet on the frequency for the past half-hour or so, and try as you might, no one seems to be answering your calls. You couldn't even pick up the automated weather observation system (AWOS) broadcast from the last airport you flew by. What's going on?
Most likely, one of four things. In order of seriousness, these are: a) The radio's volume control is set way too low; b) The audio panel is misset; c) The radio you've been using has given up the ghost; or d) The electrical system itself — or part of it — has died. Obviously, that last situation is by far the most serious. You'll have to make some big decisions when experiencing an electrical failure and, depending on the situation, those decisions may be critical to the safe conclusion of the flight.
With this as background, let's turn to some failure modes and look at how best to deal with them.
That's why it's important to include the ammeter/loadmeter in your instrument scan. Too often, it's not in our scan at all.
One indication of an alternator failure would be a discharge indication on an ammeter. Ammeters should indicate a zero charge in normal operations. A discharging condition, indicated by a minus indication on these gauges, means that the battery is running down. Why? The alternator is no longer charging it, and the battery's power is being robbed by the electrical system's components.
A loadmeter's declining — or zero — indication could be another sign of alternator failure. There's no load on the system because perhaps the alternator isn't putting out enough electricity to meet the components' demands. Other indications could be alternator-out or low-bus-voltage annunciators. It all depends on the gauges and warning systems on your airplane.
When an alternator conks out, you may have only one way to try to bring it back to life: resetting it. If your alternator is protected by an alternator circuit breaker, and it has popped, you could try pushing it back in to resume the flow of power. Resetting can also be accomplished by turning off, then on again, the alternator's on-off switch, usually a panel-type switch paired with the battery switch. If power is restored, fine. Just keep a sharp eye on the ammeter, loadmeter, or electrical annunciators afterwards. Why? The alternator may have gone off-line because of an internal fault, such as a short- or open circuit or other dangerous condition, that could crop up again. If voltage drops once more, turn the alternator off, turn off all non-essential radios, and land as soon as practical.
Some POHs suggest that you troubleshoot to determine the source of any fire, smoke, or odor of electrical origin. Here, the drill often calls for you to turn off everything on the panel and extinguish the fire. After the fire appears out, reset the battery and alternator switches and then turn on one radio or other component at a time until the bad circuit is identified or the odor or smoke is duplicated. In this way, you pinpoint the trouble spot, shut down the offending component, turn on the rest, and proceed to a nearby airport.
Again, this sounds like dubious advice. If you've had fire, smoke, or a burning odor, the risk of reinitiating the problem may be too great. It's one thing if the problem happened over mountains or on an overwater leg. It's quite another if you're over friendlier terrain where airports are more numerous.
By the way, don't forget to vent the cabin with fresh air after using a fire extinguisher. This should help eliminate any remaining toxic fumes from the extinguishing agents. Most manuals say to close any air vents after purging fumes to prevent reigniting any fire.
Night VFR is a little bit worse. With a complete electrical failure there'll be no way to turn on the runway lights at uncontrolled fields, no landing lights, no position lights to help other airplanes see you and, of course, no way to communicate your position to other airplanes — unless you've been smart enough to pack a handheld transceiver in your flight bag.
On IFR flights, pilots experiencing an alternator-out situation should consider making one final broadcast to ATC before powering down. Tell ATC that you're having an electrical failure, declare an emergency, ask for vectors to the nearest suitable airport (or use your handheld GPS), and then continue the flight using a single radio and battery power. Leave the transponder on so that controllers can issue you heading and altitude information.
Hopefully, you'll be landing soon. But in the meantime, powered-down flight in IMC can be as nerve-wracking as any other emergency. It's even worse at night. Oh, you've got several flashlights on board, right? They all have fresh batteries, right?
The biggest electrical loads are generated by voice transmissions; heating elements in pitot tubes and windshields; pulse equipment such as radar, transponders, and DME; and transient loads caused by landing gear and flap extensions and retractions. So to spare the battery, fly with one radio, keep your voice transmissions to an absolute minimum, and run the transponder only if necessary.
You often hear that a battery will last 45 minutes after it's deprived of alternator energy. But that would be for a new battery that's in tip-top condition. An older, poorly maintained battery won't last nearly that long. Put a big electrical load on an older battery and you may only have 15 minutes of electrical power. That's one more reason why landing as soon as possible is the safest recourse after a total electrical failure. You don't want to wait for the sounds of silence to learn that your airplane is voltless.
E-mail the author at [email protected].
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