Avoidable Accidents

[Larry]

No doubt many of you will have come across accounts of avoidable accidents, as in this case that came in to my possession. Sadly the pilot's name, rank, the unit and aircraft serial is not known. Incidentally I'd be interested in any explanations concerning how the aircraft engine could start.

One day an RAF pilot on a ‘jolly’ (as unofficial flights were known in the services) arrived in a Tiger Moth to visit family or friends in the local area. The Tiger Moth was left on the airfield overnight but when the pilot returned in the morning it would not start. The pilot tried a few times to get the engine started without success so the station personal also tried still without luck. I was therefore asked to help, so the aircraft was pushed in to the hangar for me to check the engine timing. The process involved lifting the magneto cover which made the system live, so the switches were moved from ‘off’ to ‘on’ and the coil starter in the engine was fully wound up. Unfortunately while I was working on the aircraft a friend of mine came in to the hangar and asked if I was coming for dinner and happened to rest his hand on the propeller but moving it just a few degrees made the coil click in to action and the engine started when I was standing between the propeller and the lower wing! Without the precaution of chocks in place, the aircraft then started to move forward and I was knocked over and dragged along by the aircraft while hanging on underneath. My friend was lucky too as he was missed by inches by the spinning prop and managed to jumped out of the way. There was now nothing to stop the Tiger Moth moving forward and smashing into the side of a Fairey Swordfish that was required for an important test the following day! Inside the Swordfish were three men working on it and they got out of it in double quick time! Luckily there wasn’t any serious damage to the Swordfish and only the fabric was ripped on the fuselage. Consequently a Court of Enquiry was convened and I was asked why an aircraft with fuel in it was allowed inside the hangar and various excuses were offered. Luckily for me the RAF pilot wasn’t supposed to be using the Tiger Moth and so he wanted no fuss and bother and hoped the matter could be forgotten, so in the end it was hushed up and not reported through normal channels!

[RSwank]

There is a long explanation here on starting such a plane here:
http://www.pilotweb.aero/techniques-...wing_1_4043093

I think the key part occurs in the discussion of the the coil spring in the magneto.

"While you are setting the propeller, a spring inside the starter magneto is coiling. (Assuming it’s an impulse mag; some have different arrangements such as ‘shower of sparks’, or none at all.) As you pull the propeller forwards, you should hear a click. This is the spring mechanism letting go, sending a jolt of electricity to the spark plug. If the timing is set up correctly, the plug will fire just as the cylinder passes the top of its stroke and is beginning its way down the cylinder. Note that it’s the un-coiling spring that turns the magneto and produces the spark, and it does so much faster than your hand on the propeller, which by itself is relatively slow. So if you have the ‘click’ impulse mechanism (most engines do), you don’t need a lusty pull. "

I think the point here is that if the prop was left in a position where the spring was coiled and ready to let go, the slight movement of the prop could release it and "fire" the magneto and thus the spark plug.