Light Aircraft Association

After experiencing a number of Rotax 912 SMD ignition module failures I am curious how many module failures others have had.

If you are a Rotax 912 owner and you've had no failures then please respond to make the figures more meaningful.

If you wish to say which aircraft they were fitted to and how many hours they had on them then feel free.

I thought mine were failing (kickback/difficulty starting when temps <10C, supposed to be indicative of weakening capacitors).
But a change of starting technique (i.e. leaving out the initial ignition-off churn to get an oil pressure indication) resolved the matter.
Don't the polarised capacitors take unkindly to non-use (i.e. loss of all charge that keeps them polarised)?
So I've entered a 'zero' in your survey.

Duncan McF.

There are some polarised electrolytic capacitors in the design but they do not generally cause any problems. It is the main non-polarised capacitor that is used as the primary charge store for the spark that causes the problem. I suspect that they are adversely affected by a combination of heat and high voltage.

There are other failure modes of the modules including failure of some of the transistors and bad solder joints.

There are various different symptoms that I have seen:
1. Module will not generate a spark at cranking RPM. This is due to a change in the sensitivity of the trigger inputs.
2. Module will not reliably generate a spark at running RPM. This can be due to failure of the main charge capacitor.
3. Module cannot be shut off. This is often due to a failure of one of the transistors in the kill circuit.