Both CDIs Failing on a rotax possible and why

[Viper]

Hi everyone it turns out that the engine failure of the rotax 912 in the technam I was flying was a dual CDI failure at the same time does anyone know if this is possible and why

 

 

[Ultralights]

for both to fail at exactly the same time, sounds either extremely unlucky, or something has been dont to cause the failure

 

 

[Guest Maj Millard]

Cranking the engine over with the spark plugs out, with IGN switches in the ON position, will zap the boxes. (plugs not grounded) Not a recommended proceedure. If the start switch is the multi positional key type, it is almost impossible to crank the engine over without also turning the IGN circuts on. Even cranking over with only one set of plugs out on each cylinder, will do it.

 

If the plugs are removed, they must be inserted back into the plug cap, and grounded positivly back to the case using either aligator clip leads or lockwire.This mistake is often made during a compression check, or when cranking the engine to check for oil pressure following an oil-change.....The ignition boxes also need a positive ground to operate correctly, without that damage could occur...As mentioned by Ultralights it would be highly unlikely both would just fail together in flight...This is by the way the type of failure reporting we need after an incident., it was initially thought or suggested that carb-ice may have been the culprit in this incident.................................Maj...

 

 

[Guest ozzie]

Under what circumstances did this happen? In flight?

 

 

[Guest Maj Millard]

In flight Ozzie, leading to a forced landing. If damaged as per my post above they could then fail, at any time.....The Rotax maintenance manual clearly states "Do not crank the engine over with the spark-plugs removed, and with the ign switches in the on position"............................................Maj...

 

 

[damkia]

I'm not totally up to speed with the wiring to/from the CDI units/ignition system, but is it run off the alternator/battery system?

 

If so, then a few of things to consider maybe a bad alternator rectifier/regulator supplying either over voltage, or negative voltage spikes via short circuit rectifier diode to the CDI's, or possibly an open circuit to the battery, allowing for higher than normal voltage to the CDI units. It is possible for all of these to co-exist (bad alternator regulator causing battery failure -> CDI's destruction).

 

In terms of fault finding, look for any common nodes between the two CDI's

 

 

[Guest Maj Millard]

Damkia, The Rotax ign circuts are self excited by generating coils in the stator/rotor generating unit at the rear of the engine. They operate independent of the battery. For instance if you have a battery master in your aircraft you could turn that off in flight, but the engine would keep operating normally because the magneto unit is still producing power, and powering the boxes.

 

If you did have need to turn off the battery master for some reason, (smoke in cabin, fire, other electrical fault) then only the items powered by the battery would become inop. Engine would be singing away producing it's own independent power.....The Rotax engine electrical and ign circut has a very high history of reliability unless damaged by an incorrect non-recommended proceedure............................Maj...

 

 

[Guest Error404]

I suspect that they failed during the flight possibly at different times but you would not know when exactly. Either way, the same result.

 

 

[Head in the clouds]

This is really great to be getting some solid information about a recent failure. I'd like to thank Swanny particularly for getting this going, please post anything more you hear about.

 

Maj, I know where you're coming from and you'll probably remember from another thread that I'm fitting a new 912 right now so I've been talking with Flood's guys and all that. I'll re-read the manual tomorrow but I'm pretty certain that cranking open circuit only has to do with potentially damaging the Rectifier/Regulator and that is why it needs to be protected by a bloody big capacitor. I may be wrong but I'll check for sure tomorrow.

 

Viper - you're probably not aware of it but you may know much more than we've heard about. When this failure happened what were you doing (flightwise)? How high? What throttle setting? Straight and level or rubbernecking at the dam? Had you been scanning your instruments? Any unusual temps or pressures? Did the engine stop suddenly or run rough first then stopped after throttle position changes? Did it rev up before stopping suddenly? All those details, and any more that you can think of will allow others who've had any similar experiences to help with the diagnosis. No-one is pointing fingers, you got down safe so that's what matters but hard facts may be the only thing that will allow this to be worked out.

 

If there is any way that mis-handling during servicing or whatever could possibly cause a double ignition failure that only manifests later, to happen, then we've got a real problem... And what history of similar occurrences is there? Do RAA compile any of this if they do hear about it? Has anyone asked Flood?

 

Also, none of this CDI ignition stuff is rocket science, every motorcycle's been using it for decades so there are hundreds of experienced people out there who would know what might have been the cause.

 

 

[Mc Guyver]

Hi everyone it turns out that the engine failure of the rotax 912 in the technam I was flying was a dual CDI failure at the same time does anyone know if this is possible and why

I know of A Technam with both CDI's failing on the ground 100HP and also a trike 80HP both also failing on the ground (would not start) Not very reassuring

I always do a mag check on shut down.

 

 

[Gentreau]

.....The Rotax maintenance manual clearly states "Do not crank the engine over with the spark-plugs removed, and with the ign switches in the on position"............................................

I've just searched the 912 Installation, Operators and Maintenence manuals (Ed3, rev0) , and there's no mention of not turning the engine over with plugs removed that I can find.

 

Where exactly have you seen this this warning Maj ?

 

.

 

 

[skyfox1]

how did you come to the conclusion that both cdi have fail.

 

Have you replace them and the engine runs fine now.

 

cheers Geoff.

 

 

[XP503]

I know it's not hugely relevant but it's spelt TECnam. There's no H

 

 

[Viper]

v

 

Cranking the engine over with the spark plugs out, with IGN switches in the ON position, will zap the boxes. (plugs not grounded) Not a recommended proceedure. If the start switch is the multi positional key type, it is almost impossible to crank the engine over without also turning the IGN circuts on. Even cranking over with only one set of plugs out on each cylinder, will do it.If the plugs are removed, they must be inserted back into the plug cap, and grounded positivly back to the case using either aligator clip leads or lockwire.This mistake is often made during a compression check, or when cranking the engine to check for oil pressure following an oil-change.....The ignition boxes also need a positive ground to operate correctly, without that damage could occur...As mentioned by Ultralights it would be highly unlikely both would just fail together in flight...This is by the way the type of failure reporting we need after an incident., it was initially thought or suggested that carb-ice may have been the culprit in this incident.................................Maj...

ery informative thankyou Maj

 

 

[Viper]

This is really great to be getting some solid information about a recent failure. I'd like to thank Swanny particularly for getting this going, please post anything more you hear about.Maj, I know where you're coming from and you'll probably remember from another thread that I'm fitting a new 912 right now so I've been talking with Flood's guys and all that. I'll re-read the manual tomorrow but I'm pretty certain that cranking open circuit only has to do with potentially damaging the Rectifier/Regulator and that is why it needs to be protected by a bloody big capacitor. I may be wrong but I'll check for sure tomorrow.

 

Viper - you're probably not aware of it but you may know much more than we've heard about. When this failure happened what were you doing (flightwise)? How high? What throttle setting? Straight and level or rubbernecking at the dam? Had you been scanning your instruments? Any unusual temps or pressures? Did the engine stop suddenly or run rough first then stopped after throttle position changes? Did it rev up before stopping suddenly? All those details, and any more that you can think of will allow others who've had any similar experiences to help with the diagnosis. No-one is pointing fingers, you got down safe so that's what matters but hard facts may be the only thing that will allow this to be worked out.

 

If there is any way that mis-handling during servicing or whatever could possibly cause a double ignition failure that only manifests later, to happen, then we've got a real problem... And what history of similar occurrences is there? Do RAA compile any of this if they do hear about it? Has anyone asked Flood?

 

Also, none of this CDI ignition stuff is rocket science, every motorcycle's been using it for decades so there are hundreds of experienced people out there who would know what might have been the cause.

Flying at approx 1750agl , rpm 4600 Straight and level , Yep at bit of rubber necking but still straight and level , Had just scanned instruments all looked good , Engine ran rough , then coughed and spluttered for approx 15 secs then died, did not rev up before stopping, when I moved the throttle in and out while it was spluttering this made no difference to performance oil good temps good .

 

 

[Viper]

I know it's not hugely relevant but it's spelt TECnam. There's no H

I stand corrected

 

 

[Guest Maj Millard]

Gentreau, Do you have the latest versions ?...Rotax continually update their stuff. I don't recall what I saw it in. I look at that stuff constantly so it could have been either line maintenance manual, heavy maintenance manual, or a service Bulletin.

 

I will look through my stuff and see if I can locate it for you though...........................Cheers Maj...

 

 

[Gentreau]

Gentreau, Do you have the latest versions ?...

I'm looking at Ed3 Rev 0 (2012), operators, installation, maintenance and heavy maintenance manuals. Searching the pdf's for "ignition" or "plugs" or "CDCI" I get no hits which refer to that statement.

 

If you can find the source, I'd be very interested.

 

.

 

 

[dan3111]

I have seen two cases of low hour 912s not staring easy and grinding away to start and after alot of testing it turned out to be the modules boxes failing at low revs only . It seems that one goes before the other then is not discovered until the second one goes down the track so then no go for you that day . It has been said it,s a good idea to only start a 912 on one mag at a time alternating between the two each time you go flying . Doing this may help pick up a crock module before the second does and you are stuck . Having said that not sure if they would give up in flight after this happens to the modules but would push my luck with a hard starting one .

 

 

[Guest Maj Millard]

The following will improve starting if you haven't already incorporated it. It's simple and does make a difference.

 

Run an electrical wire direct from the battery ground to a point on the starter body. Doesn't need to be a battery cable size wire, just a thick electrical wire. Run it and secure it permanetly. Report your findings if you try this please, and let me know if your starts get better.

 

The new rotax ignition boxes incorporate soft-start technology that the earlier boxes didn't and it has been reported that the new boxes also give better starts...You may try it temporarily for a couple of starts using your normal start methods.............................................Maj...

 

 

[Rotax Service Centre]

I'm looking at Ed3 Rev 0 (2012), operators, installation, maintenance and heavy maintenance manuals. Searching the pdf's for "ignition" or "plugs" or "CDCI" I get no hits which refer to that statement.If you can find the source, I'd be very interested.

 

.

Hi..as far as I am aware I have seen no Rotax publication that states about grounding the CDI's when carrying out maintenance proceedures other than If the aircraft has seperate Toggle type switches,then no problem,however as Maj pointed out if you have the combined starter and ign switch then you need to isolate and or ground the CDI modules.I know of only one site that states/ shows this and this is Rotax Owners Assoc Network vidio on Direct compression proceedure in which they advise to disconnect the 6pin nylon connector from the stator to the CDI'S consquently isolating them from the voltage imput during cranking..

 

As we have recently had isolated CDI module failures I aggree that it would be a good cockpit practice to attempt the first start using only one switch and alternate switches with next start as a means of checking if the CDI'S might be getting a bit tired at the low cranking RPM ..

 

Rotax needs to be aware of field problems and the more imput from Forums like these can only be to every operators advantage.Thats my opinion anyway!!

 

Safe and happy sky's..Richard

 

 

[storchy neil]

or a service Bulletin i think it was a service bullitin maj i have read that some where neil

 

 

[Guest Maj Millard]

Yes, I do frequent the Rotaxowners .com site a bit, and Ido feel I have seen it mentioned there. But also sure Rotax mentioned it somewhere too...I've looked but can't find it...I think it was recent and probabily within the last 12 months.......................................Maj...

 

 

[Mriya]

I have seen a dual ignition failure on a 912 engine. In that case it was due to the engine not being kept up to date with SB's. Early engines had the 'p' leads routed in a common harness where the l & r leads could chafe together and ultimately take out both systems.

 

Current harness design maintains separation of the 'p' leads and eliminates the possibility of dual ignition failure from this older design flaw.

 

Owners of older rotax engines should ensure that they have addressed this issue, otherwise a dual ignition failure is a possibility. As always, owners need to understand and keep up to date with all SB's if they are to ensure serviceability of their aircraft / engine.

 

PS. The owner of this aircraft described, had made some efforts to ensure serviceability via a third party, but it seems this SB had still been missed. Fortunately this failure occured on the ground during testing (new airframe with an old engine fitted) before the final inspection was complete.

 

 

[dazza 38]

FACT, I flew the aircraft in mention about 3 days prior to the engine failure. FACT - I always do a CDI ignition check at 3800 RPM before take off. FACT- I ALWAYS do a CDI check prior to engine shut .The CDI's & engine were working fine when I flew her previously 3 days before the engine failure. AND everybody who hires aircraft from this particular company always do a CDI check. Well the ones that I have witnessed.