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FlyingSafely.Com Electrical
Failure At Night Read Responses At The Bottom of This Page We study systems and systems failures in ground school and in flight training. Such system analysis may seem to be academic and theoretical, but there is a practical application to all that information. Most of the time, everything works just fine on an airplane. After all, there are 100 hour inspections on aircraft that are used for hire and annual inspections for non-commercial use general aviation craft. So, when the ammeter shows a charge you tend to take it for granted that it is true, but what if that instrument is not telling the truth? Such was the case when our training flight began from our home airport, AAA, enroute to Coles County Airport (MTO) about 5:00 PM in early February. The early part of the flight was uneventful until reaching the Decatur VOR at 5,500 MSL. It was then then I noticed the lights on the Nav Com started a rhythmic dimming and brightening. The CDI also joined the dance. Each time the lights would dim the needle would wobble. Checking the ammeter, we still showed a happy little charge going into the electrical system. What's going on? The master switch has both sides toggled on, the alternator circuit breaker is in and the high voltage light did not illuminate. As we proceeded to Mattoon, it became apparent that we were losing electrical power. Now the CDI needle was really jumping and the radio communications with Champaign Approach became increasingly distorted. Just as we changed frequencies and squawked 1200 with Coles County airport in sight we began to shut down all unnecessary electrical equipment. Landing light, Dome light, panel lights, (we were using a flex head pen light to illuminate the panel.) We clicked the CTAF frequency five times to bring the lights up and
they responded. That was our last radio transmission. Over the headsets there
was a kind of scratchy whirring sound that indicated the rig had bit the dust.
Now we have no power remaining in the battery and, obviously, the
alternator had failed. Nonetheless, our happy little ammeter was showing a
positive little charge. It might as well have been a little yellow smiley face
inscribed with the words, "Have A Nice Day". It is a dark night. The city
lights blink below us as we descend. The student asks "Should we call unicom?
Should we respond?" "I don't think we can," I replied.
The runway lights are still on as we enter a left crosswind for runway 24. I inform the student that I have the airplane and I am studying the distance and angle of the runway below in order to determine when to turn downwind. "There's an airplane below us," my student declared. "Below us, where, going which way?" I inquired. "Going into the runway. Looks like he's going to land." In the distraction of the electrical failure, looking at the runway lights, trying to figure out what else we could do, I had not maintained vigilance looking out the window to the right. There, below us concealed in the mixture of the lights of Mattoon and surrounding area were the lights of an inbound aircraft headed straight in for runway six. The winds were previously southwest at 8-10 knots, but had become light and variable after darkness fell. The other aircraft was landing with a slight tailwind the opposite direction of our intended landing. He flew under us descending to the runway while we were still showing 1800 MSL. The field elevation was about 700 feet, so we were approximately 1100 feet above the ground. I would say we had about 500 feet of vertical separation. We had no position lights, no landing light, no radio, no transponder, and no flaps (they are electrical). As we entered downwind to land, we had a new problem. The other aircraft did a touch and go on the runway we intended to land on. That meant we would be head to head with him on his climb out. The pattern is also right traffic on the reciprocal runway. We kept our eye on the other plane and lowered the nose of our stealth machine. I wanted to be well below his pattern altitude as he climbed out. There was no way he could have known we were there. It was up to us to stay out of his way. Fortunately, he did a straight out departure and we slid in under him the opposite direction on our left base to final. Without flaps, without lights, with radio, we descended to the runway. It was a uneventful landing as the wheels touched between the glow of the runway lights on each side of us. Blue lights of the taxiway led us off the runway, and mercury vapor lights reflecting on the tarmac let us know that the surface was clear to taxi to the ramp. We taxied up and checked everything one last time. Still nothing we could do would effect a change. The happy little ammeter showed a happy little charge. (LIAR!!!!) We got out and checked the alternator belt. It was intact. Some of the best spaghetti sauce on the planet earth is served at the restaurant at Coles County Airport. We sat and talked and ate two helpings (It's all you can eat), while our fellow flight instructor flew his Cessna 172 from Lincoln to pick us up. We had a wonderful and comfortable flight home. The trainer was left tied down at Coles County to be picked up in a few days for maintenance. Turns out the alternator was completely gone and the electrical load at night simply ran the battery down before the landing occurred. The culprit, aside from the defective alternator, was the inoperative ammeter. It was that second link in the chain that put us at some risk that winter evening on our first night cross country training flight. What did we learn from this experience? If you have an ammeter that is always showing you the same charge, look at it with suspicion. It won't really matter if it lies to you as long as the alternator is actually working. Everyone is happy. The night the alternator quits and you have no warning, the lie becomes a threat. How about a new digital ammeter, or just an analog that works? Keep flyingsafely, Larry Collins, Editor Postscript: It is interesting to note that an ammeter is not required by the regulations for a Part 91 operation. Hmmmmm. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ We welcome your comments and reactions to this article. Responses: A well meaning pilot offered a suggestion that with a split switch master, the battery could have been shut off with only the field of the alternator left engaged. He was thinking that when the alternator failed, the aircraft lights would go out immediately letting you know the alternator wasn't working. The only problem with this suggestion is that it is not possible to do this on this Cessna 152. Cessna designed the split master switch so as to not allow this configuration. The battery can be switched on alone, but the alternator field cannot be engaged separately from the battery. Thanks for trying.. Editor Whoa! That must have been a pretty tense moment! After reading the
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by Larry Collins
