Alternator Failure

Just last Friday, I had another alternator failure. In terms of equipment failures, charging system failure is the one I’ve seen most often. I’ve had a dozen or more failures in 7000 hours of flying. Depending on the situation and airplane, this failure can be anywhere from a non-event up to a serious emergency. Let me describe my recent experience on a VFR instructional flight and discuss some other possible scenarios.

Alternator Failure on a VFR Flight in Los Angeles

I was flying with a new private pilot in one of our club’s 172s, doing part of the Tour of LA. We had already flown over downtown LA, Dodger Stadium, the Coliseum, the Hollywood sign and done the LAX SFRA (Special Flight Rules Area). We were just about to circle the battleship Iowa when he noticed our engine monitor (a JPI EDM-730) was flashing “BAT 11.4” in red. The engine monitor has a configurable voltage at which it will show this alarm, indicating you are most likely operating on battery only. The plane’s red warning light was not illuminated, but the ammeter did show a slight discharge. We checked all the circuit breakers (none were popped), we confirmed that the alternator Master (Alt) switch was on. We alerted the Torrance tower controller that we’d had an alternator failure and were heading back to El Monte. The controller asked if we required any assistance. We asked for a frequency change to Long Beach tower to get us on our way.

At this point, we turned off our second radio and turned off the plane’s lights. The goal in reducing the load on the battery is to increase the amount of time your remaining battery capacity will last. Just that reduction in load made the indicated battery voltage jump about 0.3 volts. I was reasonably sure we had caught the failure soon after it occurred and were only about 20 NM from our home base. With a healthy battery, I expect at least 30 minutes at reduced load.

We called Long Beach and advised them of our alternator failure and asked for a transition northeast to El Monte. They approved our transition above 2000′, asked if we needed any assistance, and gave us an early frequency change to contact El Monte tower.

We contacted El Monte tower while still about 15 miles south and they offered a straight in approach to runway 1, even though runway 19 was in use. We accepted (after conferring that winds and runway length were acceptable for a downwind landing) and eventually were cleared to land and told to taxi with the tower controller directly to parking. All of this was to help minimize our time running on our battery (it helps that the EMT controller we were talking to is a pilot who would know more than the average controller about failures). We made it without incident to our parking. Our indicated voltage only dropped 0.1V further.

So, why were we advising each controller of our failure? This helps them understand that a loss of communication or transponder is possible and helps ensure they understand there’s some urgency, though I wouldn’t call it an emergency. Most of our flight was after we were in contact with EMT and they would have handled things smoothly had we lost communication sometime after our initial call. You should also notice that each controller was very willing to do whatever they could for a positive outcome in our flight – I have found that to be universally true when you are having airplane problems and you let them know about the problems.

We could have also turned off our transponder and reduced our load even further, but I felt that move was unnecessary and more likely to cause problems in the busy airspace in which we were operating – through Long Beach class D and under the LAX class B on the way back.

Lastly, we didn’t try the step of turning off the avionics, as well as the battery (Bat) and alternator (Alt) Master switches. This can occasionally reset an alternator and get it working (it has worked once for me).

Why didn’t we just land at Torrance? That would indeed be the absolute safest solution – get down as soon as the problem is detected. I do worry when pilots let get-home-itis fool them into flying with failing systems that get them in more trouble later in the flight. However, I  was very confident with the distance to fly and the rate of battery voltage change that we had plenty of capacity to get us to our home base. Don’t try this with anything engine or fuel related or in worse conditions. You always need to understand the nature and impact of any systems problems and if you are unsure, it is safest to figure it out on the ground at the nearest airport.

Charging System Failure

I called this failure “charging system failure” since all we can really tell is that the battery is no longer being charged by the alternator. This can be caused by an actual failed alternator, or voltage regulator failure, or by a broken alternator belt, or even by a broken wire. I’ve had every one of those failures, but the diagnostic steps and eventual outcome are basically the same. You should refer to the checklist in your airplane’s POH or AFM for the recommended steps for your particular airplane.

VFR flight failures

In most cases we should be able to fly a plane safely in day VFR conditions without electrical equipment (remember that’s how many older planes have to fly). You should be able to keep the airplane under control and navigate to a nearby airport without such aids, but those are skills you have to maintain. In some planes the challenges will be the need to fly an out of trim airplane (if only electric trim and the power goes out) or to do manual extension of normally electrically driven gear systems. If you have electric flaps, when was the last time you practiced a no flap landing? Landing at a nearer, non-tower airport may be a safer alternative from a communications standpoint if the battery dies (more in another article on communications failure).

Electrical loads – what matters?

Some electrical loads matter more than others. Anything that transmits will use more power than receiving. This is part of why turning off your transponder and DME and minimizing your radio transmissions are good ideas when trying to conserve battery power. Lights are also big power draws – generally the bigger/brighter the light, the bigger the load. Old filament bulbs use much more than modern LED bulbs. Any motor (flaps, gear, trim) will also tend to be a big user of power. Electric pitot heat is a huge load, but if you are in conditions where it is needed, you have a tough decision to make. The size (numbers of amps) of the circuit breaker the equipment is attached to is a good indicator of how much power that equipment can use. You may also want to conserve extra power for use of something later in the flight, like a light for actually landing at night or putting the flaps or gear down before landing.

What if you didn’t notice the failure?

If you don’t notice any of the indications of charging system failure (do you know what they are for your plane and do you regularly check?), you will eventually notice that some electrical equipment starts to work poorly or intermittently. Often the first indication then will be inability for a controller to hear your transmissions (since they are getting weaker with drops in battery voltage) or radar contact will be lost as your transponder’s replies are weaker, or lights and displays will appear dimmer than normal. At this point you are very likely to get to deal with complete loss of your electrically powered equipment.

What if you were flying IFR and in IMC?

Now, charging system failure becomes much more serious. Consider the possible loss of some of your instrumentation (turn coordinator on many planes), as well as loss of navigational and communication capability (Comm, VOR, ILS, GPS, etc.). I would get vectored immediately to the nearest possible airport or to an area of VFR conditions.

What about planes that are all electric?

My charging system failure just before this one (about a month ago) occurred in a Cirrus SR-22. This airplane is nearly all electric. Because of its greater reliance on electricity it has dual power buses (primary and essential) as well as dual alternators. The loss of a single alternator was really a non-event, but caused us to cut our training flight short. You should be very familiar with the possible failure modes of your airplane’s electrical system.

What if this were at night?

I would still reduce load (and probably turn most lights off), but with a goal of landing sooner to help ensure I have a landing light I can turn on for my landing. I do always carry a headlamp and handheld radio that would help me be more comfortable in such failures just to at least see inside the plane and be able to communicate.

2 thoughts on “Alternator Failure

  1. Thank you for sharing this experience and your analysis. I greatly appreciate being able to learn from others’ experiences with failures, instead of waiting for them each to happen to me personally. 🙂

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