Page 17 - Volume 14 Number 4

with a worn-out one, you can see the center hole is much larger in the old igniter – the gap is too wide. Additionally, the electrode in the old plug is severely worn.
You might be wondering, since there are two igniters per engine, why would both igniters go bad? I suspect they go out one at a time. Let’s say the igniter box is a tad low on amperage – it’s within limits and doing its job, but the spark doesn’t travel quite as far. As the igniters wear down, the gap widens and one plug fails. At this point maybe the starts are a slightly slower or a tiny bit hotter, but these differences are negligible. So many times, gradual degradation in performance escapes our attention. It’s just a matter of time until the other plug fails and you have a no-start situation. That gets your attention.
Something that accelerates ig- niter wear is leaving auto-ignition on all the time. The checklists in the POH for pre-takeoff and pre- landing specify when the auto- ignition switch is to be turned on as a safety measure in the event of engine flameout. I’ve met many a King Air pilot that worries they will forget to turn their auto-ignition on before takeoff and before landing, so they turn it on early and leave it on. They know that the auto-ignition system goes off automatically once 400 foot-pounds of torque is reached after takeoff, and likewise, it comes back on when the torque falls below
that mark. At shutdown they turn everything off.
There is nothing wrong with doing this, particularly from a safety point of view. The downside to this procedure is that the igniters on each engine are furiously snapping away throughout the whole pre- takeoff routine, the taxi out, the taxi in and the pre-shutdown routine. This is a lot of wear and tear on the igniters.
When I had my shop, I had some customers that could not get 300 hours out of an igniter, and I had others that would get 600-700 hours. I have no problem with anyone that keeps auto-ignition engaged in this manner. I am not being critical and I don’t want to mess with anyone’s routine. All igniters wear out eventually, so it never hurts to have a spare one stashed in your aircraft. When it comes to ignition failure, igniter plugs are the number-one cause in my book.
Worn Igniter Leads
Igniter leads are disconnected at each Phase Inspection in order to inspect the igniter plugs. These leads have an insulator on the end that goes into the igniter plug. The insulator has a tendency to stick to the plug. When your mechanic removes the nut that secures the lead, he or she often must tug and twist the lead to disengage it. The insulator eventually breaks and this
A comparison of a new igniter (left) and a deteriorated one (right), which portrays the wider gap in the middle and the worn-down electrode.
APRIL 2020
KING AIR MAGAZINE • 15