Page 16 - Volume 14 Number 4

MAINTENANCE TIP
Engine Won’t Start?
by Dean Benedict
When you hit the Start/Ignition switch and the engine spools up but fails to light off, what do you do? Is it a fuel problem, an ignition problem or both? Obviously if your engine gauges indicate fuel is flowing, then you’ve got a problem somewhere in the ignition system. I’d have a tidy sum in the bank if I got a dollar for every time someone suspected the ignition box as the reason for ignition failure. I don’t know where it got such a bad rap. In my experience the ignition box is the least culpable of all the components in the ignition system. But I’m getting ahead of myself.
Some would argue that if you don’t hear the igniters snapping, you know it’s an ignition problem. Unfortunately, the noise of other aircraft running nearby or taxiing to and fro makes the snapping hard to hear. Chances are (if Murphy’s law has anything to do with it, and it usually does), you are at an unfamiliar airport, far from your trusted mechanic or a shop that knows King Airs. In the above scenario, you can try the auto-ignition switch to see if you get spark. If you do, the engine starts up and you now know that there is an issue with your Start/Ignition switch or its related relays. If there is still no spark with the auto-ignition switch, then there is an ignition problem at the engine.
Be sure to check your annunciator panel. Go back to the Start/Ignition switch. (Don’t forget to clear the engine of fuel if you’ve already attempted a start.) Turn it on and see if you have an ignition light. It could be yellow or green, depending on the model of your King Air. This light is wired directly to the positive lead at the cannon plug on the ignition box. If your annunciator panel shows the ignition light in start-ignition mode or auto-ignition mode, then you know power is going all the way to the ignition box.
So now what? Your suspects are the ignition box, the igniter leads, and/or the igniter plugs. Believe it or not, most of the time it’s going to be the igniters. They get checked at every phase, but if they are within their designated wear limit, they are not replaced. Igniters are expensive and you want to exhaust their useful life before putting in new ones.
Worn Igniters
Igniters wear down to a point where the gap is too large and the spark fails to jump across. There is a maximum allowable diameter for the center hole surrounding the electrode. In the photo (right) comparing a new igniter
14 • KING AIR MAGAZINE
APRIL 2020