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Stuck Starter Contactor - Lesson to learn

No matter how much you think you know, there are always lessons you learn by experience. Follow me through….

- Flatten battery by testing systems
- Try an engine start but get click, click, click won’t turn over and abort start asap
- Remove and charge the battery
- Turn on the master switch and prop rotates!

You get some shock when you turn on the master, and the starter engages. The contactor had clearly stuck, but it’s best not to learn such when an aircraft is in a hangar or a tow bar is still attached. That is why on an old school checklist you:

- Shout clear prop
- Turn on master

There is also an AD 77-12-08 on some Cessna’s where you need to check if the prop rotates upon the application of ground power. My kid was on the airfield at the time, thankfully nobody turned on the master switch when he was about to check anything in the hangar. No harm done but big lesson learned.

Buying, Selling, Flying
EIBR, Ireland

Good nothing bad happens !

The reason one check mag drop on L/R before shutdown is make sure mags are NOT LIVE when key switch is OFF position, by turning the mags off the engine will normally not get a spark, if there is a broken P-lead, switch OFF will not be grounded and the engine will be on live mags (or simply just to check the key is not stuck before pulling mixture back )

ESSEX, United Kingdom

I remember being a kid at the local airfield, and the local hero pilot/mechanic shouted at me for starting in the arc of a propeller of a parked aircraft looking in at the engine. Now 32 years later I understand his wisdom. Even though I am around them the whole time, it never fully rang home with me the prop could rotate my mistake.

Buying, Selling, Flying
EIBR, Ireland

After 18 years of Share/ownership I became complacent regarding checking mags,masters, mixture before moving or touching a prop.
I was so diligent at always ensuring they were set correctly at shutdown.
The very 1st visit to a club environment for many many years was for a sortie in a club/school aircraft.
After pulling the aircraft out (under instructions from an instructor) I began the walk-around and found the mags to be ON.
Phew, lucky escape.
It may not run but a single cylinder combustion “pop” may be enough to kill you if you were that unlucky.

Private strip, Essex (not mine), United Kingdom

Yes putting the keys on the dash is not a bad habit. I made a similar mistake with a new plane, all excited to give it a wash. Taxi up to the power washer, killed it with mixture, turned off the master but forgot the mags and pulled it forward by the prop. Nothing happened but you feel like a prize ass.

The aeroplane has no feelings, it could bite your head off at a whim for being stupid.

Buying, Selling, Flying
EIBR, Ireland

Thanks for sharing these insights William.
The off-mag check is something (with others) I learnt the reason long after my license. It shouldn’t be the case.


This is a great thread. What a warning!

Stuck relays are an insidious problem. I have just replaced the TB20 ground power relay. It was stuck, as they usually are, in the resting position. Nobody would realise it, until they get a flat battery, miles from home, but there is an external starter pack available. It won’t work… I fly with a spare one of these in the boot (along with a spare vac pump and enough other bits to build another TB20).

Shoreham EGKA, United Kingdom

WilliamF wrote:

Yes putting the keys on the dash is not a bad habit.

It’s a good mental reminder that one has turned off the mag, but most keys can be removed from the mag switch regardless of switch position …. just saying.

LSZK, Switzerland

most keys can be removed from the mag switch regardless of switch position

Wasn’t there an AD on the mag switch, exactly to prevent this?

Shoreham EGKA, United Kingdom
What´s the big wisdom to kill the engine with the mixer anyway ?? I know we did it while training for PPL. Our radial has no mixer anyway , just a barometric automatic mixture device on the carb. So there is no other way to stop the engine but by the mag switch – or in emergency by closing the fuel tap. To prevent kickback and reverse running you open the throttle to full when switching off the mag, so it is unlikely to have hot mags while pulling through the radial to clear oil in cylinders. Nobody turns off fuel on car engines for stopping them and wet spark plugs don´t happen on a hot engine just by stopping it with mag off. Also the sparks will not clean much by setting mixer to full lean when stopping – so why . . . . Vic
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