Stuck starter contactor: what to look for

[photofly]

I just had a lightbulb moment from which someone else might benefit.

Last week I had the starter contactor stick closed, on one of my aircraft, after starting the engine. I didn't notice immediately, but I could have.

Here's what happened: after doing the 24 month static check, I wanted to make a short flight. After start, the ammeter showed a very high rate of charge. No surprise, I thought - we've had the master on for an hour running the transponder, so no wonder the battery needs a little top up.

Queueing for takeoff, the radio started behaving oddly, then died (curiously the high frequencies went out first - I lost the ATIS on 133.6 before I lost the ground on 121.7, then tower on 118.2) - so I taxied back to the ramp. I shut down and realized I had a flat battery. So out came the charger, and I recharged it overnight.

The next day, as soon as I switched on the battery master the prop started to turn. The starter contactor was stuck in the 'energize' position.

A few days on I realize why the ammeter had shown a high *charge* rate when the engine had started. The starter motor is powered through a thick cable that bypasses the ammeter. With the starter motor continuing to run after the switch was released it was draining the battery fast, and the generator was doing all it could to replace the charge back into the battery, through the ammeter, hence the high charge current.

So there's a lesson: if you see a much higher charge rate than you expect after starting the engine, consider that the starter motor might still be running.

Mine must have been going for five or six minutes until I shut down or it drained the battery totally; time will tell if there was any overheating or life-shortening. If I'd recognized the symptom I could have shut things down within seconds.

[jg24]

Interesting.... thanks for sharing.

Did you hear or notice any odd noise? Was the starter fully engaged onto the ring gear?

[confusedalot]

Now that is interesting. Am I correct in assuming this was on a piston engine aircraft?

The only reason why I am asking is that during my turboprop time, the equipment had a starter/generator setup, and after the start cycle you would immediately know there was a problem via caution lights, since the generator feature would not engage.

Never happened on a piston, lucky I guess.

[photofly]

Yes, a SEP. Lycoming O235 engine.

I don’t know the status of the ring gear at the time. It looks undamaged now though, and it still works. There probably was an odd sound but I didn’t hear it over the engine noise. I’m probably quite lucky the battery quit running the radio before I left the ground, both in terms of ATC inconvenience and possible mechanical damage.

[PilotDAR]

A stuck starter contactor is a serious problem in any piston engine - so much so, that in the UK, it has been a requirement to have a "starter engaged" warning light, to indicate such a failure to the pilot. Fortunately in the Lycoming, and small Continental designs, there is still an over running clutch in the starter to engine drive line, so the starter motor continuing to be energized will not result in its being driven by the engine, the over running clutch will slip as intended first. (Otherwise, the engine, when it first kicks to life, could not accelerate faster than the starter is turning it). So, energized stater is not good, and will ruin that over running clutch.

Much more serious, is this condition in any larger Continental engine with a "starter adapter": O-300D, IO-360, all 470/520/550. You know you have a starter adapter if the starter motor axis is at right angles to the engine centerline. In the case a stuck starter contactor in this arrangement, the clutch inside the starter adapter, which is a cunningly designed coil spring (about like a super dense slinky), will become red hot, distort all over within the housing, and ultimately fill the whole engine with steel bits via the common engine oil. The adapter will be scrap, and expensive repairs required. The problem is that the pilot probably will be unaware, and it will only be at the next start attempt that this damage will be found. Preventative starter contactor replacements are low cost by comparison. The are good quality, and low quality contactors, so use the specified high quality ones. Canadian Aero Manufacturing in Orillia sells starter engaged light warning kits.

[photofly]

A stuck starter contactor is a serious problem in any piston engine - so much so, that in the UK, it has been a requirement to have a "starter engaged" warning light, to indicate such a failure to the pilot.

In lieu of which, look for a continuing excessive rate of charge immediately after engine start.

[pelmet]

A stuck starter contactor is a serious problem in any piston engine - so much so, that in the UK, it has been a requirement to have a "starter engaged" warning light, to indicate such a failure to the pilot.

In lieu of which, look for a continuing excessive rate of charge immediately after engine start.

Correct. The current should start to decrease instead of staying the same. But how quickly it should decrease is the big question and probably varies from situation to situation. If it is remaining engaged....it might just be best to turn off the master switch.

[CFR]

A stuck starter contactor is a serious problem in any piston engine - so much so, that in the UK, it has been a requirement to have a "starter engaged" warning light, to indicate such a failure to the pilot. Fortunately in the Lycoming, and small Continental designs, there is still an over running clutch in the starter to engine drive line, so the starter motor continuing to be energized will not result in its being driven by the engine, the over running clutch will slip as intended first. (Otherwise, the engine, when it first kicks to life, could not accelerate faster than the starter is turning it). So, energized stater is not good, and will ruin that over running clutch.

Much more serious, is this condition in any larger Continental engine with a "starter adapter": O-300D, IO-360, all 470/520/550. You know you have a starter adapter if the starter motor axis is at right angles to the engine centerline. In the case a stuck starter contactor in this arrangement, the clutch inside the starter adapter, which is a cunningly designed coil spring (about like a super dense slinky), will become red hot, distort all over within the housing, and ultimately fill the whole engine with steel bits via the common engine oil. The adapter will be scrap, and expensive repairs required. The problem is that the pilot probably will be unaware, and it will only be at the next start attempt that this damage will be found. Preventative starter contactor replacements are low cost by comparison. The are good quality, and low quality contactors, so use the specified high quality ones. Canadian Aero Manufacturing in Orillia sells starter engaged light warning kits.

Ah the Brits!