Looking at 912 failure modes......

[Guest Maj Millard]

Following on to the post reporting the Tecnam/912 failure recently I'd like some input on any 912 failures you've experienced or heard of.

 

Personally I've probabily flown with ten or more different 912s in the past 15 years, and done around 500+ hours on my own 912s in the Lightwing.

 

Additionally as an unlimited L2, I see a lot of other peoples' problems when they have engine dramas.

 

Bearing in mind that around 60% of all engine failures are fuel related !!....including running out of it.

 

In my experience I would suggest the following list are the most potential failures you may expect with a 912. Listed as most potential first, to least potential.

 

1. Engine stoppage due to carb-mount rubber failure or leakage.

 

2. Engine stoppage, or rough running due to pilot leaving fuel boost pump on ( exceeding max carb operating pressure, causing flooding or over-rich mixture).

 

3. Engine stoppage due to incorrect carb settings or adjustments.

 

4. Ignition failure (normally detected on ground during mag checks)

 

5. Carb icing due to nil carb heating or improper usage by pilot.

 

6. Internal mechanical failure due to incorrect oil usage.

 

7. Mechanical fuel-pump failure.

 

Explanations: 1...The early carb-mount rubbers were a harder compound-they lasted longer. The newer one's are softer, and seem to want to crack and fail around 250 Hrs. I am on my third set at 700 hrs TT -all failures detected during ground inspections.

 

2...Rotax have recommended minimum and maximum fuel operating pressures for the Bing carbs. Leaving elect boost-pumps on in some installations can overpower the carb bowl floats, and cause over rich mixture to the engine. Fitting and monitoring a fuel-pressure guage is recommended. 3...The Bing carb is as basic as they get, however people still tinker with them unnecessarily, and operate them with incorrect adjustments or settings- refer to Rotax maintenance manual for correct settings and adjustments. 4...The Rotax 912 ign boxes produce around 40,000 Volts. Cranking engine over with spark plugs out, and ign switches on, does not allow this high voltage to ground via the spark plugs, and will ruin the solid state ign box. Normally one circut completely dead during mag checks. Inflight ign failures are rare. If cranking engine for oil pressure during initial start or after oil change, ground ign leads/plugs and ensure ign switches are OFF!...5....Carb heat systems should be fitted, and used when required. All carbs are subject to icing in the right conditions. 6...The Rotax engine and gearbox require a synthetic fortified, approved oil for reliable operation. Use of incorrect or non-approved oils will cause damage which can lead to failure. 7...Mechanical fuel-pump failure is rare, but when it occurs can cause engine stoppage. A friend recently had one fail at 250 hrs. Check pumps regularly for leakage from seep hole, and replace if found........................................................................................Maj....

 

 

[turboplanner]

Of the 8 forced landings I extracted from about half the Pilot Notes between May 07 and March 12, these were the reasons given:

 

1. 912A Carbs overflowing

 

2. 912 Vapour lock

 

3. 912 ULS Tailpipe separated

 

4. Oil leakage around filter

 

5. Spark plug fell out

 

6. Circlip

 

7. Oil Pressure

 

All except 6 and 7 fit into the heading of poor maintenance practice or poor engine installation

 

Item 6 doesn't specify whether the engine had been rebuilt, but that's what I'd expect, and the rebuilder wasn't quite up with some of the traps of circlip placement

 

Item 7 is frustrating - not much better than reporting that the aircraft "had a forced landing", so we don't know

 

 

[eightyknots]

Of the 8 forced landings I extracted from about half the Pilot Notes between May 07 and March 12, these were the reasons given:1. 912A Carbs overflowing

 

2. 912 Vapour lock

 

3. 912 ULS Tailpipe separated

 

4. Oil leakage around filter

 

5. Spark plug fell out

 

6. Circlip

 

7. Oil Pressure

 

All except 6 and 7 fit into the heading of poor maintenance practice or poor engine installation

 

Item 6 doesn't specify whether the engine had been rebuilt, but that's what I'd expect, and the rebuilder wasn't quite up with some of the traps of circlip placement

 

Item 7 is frustrating - not much better than reporting that the aircraft "had a forced landing", so we don't know

I wonder how (4) would cause a forced landing?

 

 

[Guest ozzie]

4) low oil pressure from dumping oil, possible smoke in cockpit from oil hitting exhaust and oil on windcreen could be some reasons.

 

 

[turboplanner]

Eighty, if you cross thread the filter (hard, I know, but I've done it) or don't seat the gasket correctly, oil at full pressure can really squirt.

 

 

[Guest Maj Millard]

So mainly as I see it TP, those are mostly pilot/ maintenance failures ?...................Oil pressure readings on the 912 can read pretty low, but still be within range. Don't know that I've heard of too many that have really lost oil pressure in service, except where the oil has been allowed to go below minimum quantity required. And again operator error ?..................................Maj...

 

 

[Guest Maj Millard]

Oil filters and spark-plugs especially, should always be started first by hand. Once it is properly engaged a few threads by hand on, or in, the threads you can then, and only then, put a tool on it and finish the job.....................Maj...

 

 

[turboplanner]

Yes, 6 and 7 also could be maintenance issues as well, but we just don't have the data.

 

 

[Guest Maj Millard]

Thanks for your input Turbo. I have noted that the incident info we get in the mag is really edited to the bare minimum. I submit reports often and have noticed this, often my incident/accident reports will be more in -depth, but it all gets lost in the editing................................................Maj...

 

 

[turboplanner]

I'd rather get rid of the Magazine and replace the cost of that with reasonable investigations and reports on the RAA website for permanent reference.

 

 

[eightyknots]

Eighty, if you cross thread the filter (hard, I know, but I've done it) or don't seat the gasket correctly, oil at full pressure can really squirt.

Sounds nasty. Hopefully this becomes evident whilst still taxiing rather, say, 15 seconds after completing the takeoff roll.

 

 

[turboplanner]

Well usually as soon as you start the engine - very obvious in a car if you reverse out of the shed.

 

 

[facthunter]

There was also a documented failure of a 912 flying to Narromine when a hydraulic lifter failed requiring an outlanding. I saw another low hours engine returned for reassembly for an "O" ring left out and subsequent oil leak. Other problems are carb rubbers and exhaust system cracks. Inspection finds these.. I have had coolant discharge when on a long trip and the day became very hot. Land and adjust airflow. These engines do not require much fiddling with the main core of the engine unless you strike the prop. against something, so they give less trouble. Nev

 

 

[Guest Maj Millard]

Just had a chat with a rather interesting dicky-bird who's in the know. He/she reckons the first 912is (fuel -inj) engines into this country may well end up in Brumbys ?......also, that a private large aircraft manufacturer in Germany with no connection to Rotax, had done identical, side by side, in flight testing with a normal carb 912, and a new 912is. Very identical aircraft, air, fuel etc and state of the art monitoring equipment. Turns out the figures they ended up with were far better that those quoted by Rotax on power, fuel consumption etc.......this could certainly be one to watch.

 

Also on mechanical fuel-pumps for 912s. The original Pierburg pumps fitted are pretty bulletproof and reliable, but the later AC manufactured ones are not.................the newer latest style pumps seem to be doing just fine so far......then I asked what he though was the thing causing most failurers in 912s, he said there isn't any !!...but suggested that people messing with the carb settings/adjustments was up there on the list....................Maj...

 

 

[Guest Maj Millard]

On oil leaks.....................years ago I was walking down a ramp at a large Californian airport. A person had just pulled a Cessna 152 out of the hangar after a 100 hourly, and after chocking it, preceeded to fire the engine up for a run with the cowls off (normal proceedures so far after maintenance). When it fired up I immediatly noticed a large agressive stream of nice new oil coming out of the rear of the engine. It was then blown downwards and exited underneath the aircraft belly, unseen by the operator. At the rate it was being expelled it was going to all be over in about 20 seconds !!

 

I indicated to the person to shut the engine down which they did. Upon inspection the maintainer had simply forgot to spin on, the spin-on oil filter !!........................true............................................Maj...

 

 

[facthunter]

The new motor appears to be a complete redesign. Very high tech. Back to a specialist repairer if not running right. Very sophisticated engine and a lot more expensive than the current one. It's probably a good thing. I'm a bit old fashioned. I don't mind fuel injection and can put up with a pretty crude one that I have to set. Those older systems light up the grass under the engine sometimes if you are not careful. My generation were happy to move knobs/levers. Todays people want it digital with sensors and microprocessors. Nev

 

 

[Teckair]

I had a 912 80 hp stop shortly after take off once, turned out the owner had just extended the carby breather / overflow tubes out the bottom of the cowl. As soon as we hit 90 kts the flame went out. You should have atmospheric pressure inside the float chamber.

 

 

[facthunter]

Teckair, you are not the only one to find out what that tube can do. Nev

 

 

[Guest Maj Millard]

Good one treckair, Yes best to just leave those little plastic tubes the way they come, tucked under the fuel bowl retainer clip. Many people misunderstand their main purpose which is to allow ambient pressure in the carb bowl. Instead they think they are fuel overflow tubes (secondary purpose only) and route them all over the place, into areas of negative pressure. Sounds like you got some first hand experience with that !........................................Cheers,................. Maj...

 

 

[Ultralights]

i think the carby rubber mounts cracking issue can be greatly effected by the installation in each aircraft, i have noticed with my savannah, that the carby rubber mounts were still in very good condition with no sign of cracking after 800hrs. and yes, the mounting was removed, and inspected inside and out. yet the mounting of the carbys in the school tecnam have been showing signs of cracking every 200 hrs. the difference i believe is the extra support offered to the carbys themselves via the aluminium air box that itself is mounted at 2 points on the aft of the engine block, therefor the carby is supported from both ends, and is attached to the engine at both supports, so the carby cannot move independently of the engine via G force, or engine movement. whereas the Tecnam carbys are only supported at the intake manifold end. and are feee to move with vibrations and G loads. also the mounts are supporting the weight of the air filters and the cabys themselves.

 

 

[dazza 38]

I have Sting aircraft on my facebook. A owner fitted a 912is in his aircraft.They had a engine failure & had to put it down on the beach. Not sure exactly what the out come was, but the general chit chat was that the fuel system was the cause.They had plenty of fuel on board. Could have been the the way the fuel system was set up. She is flying again now.

 

UPDATE- apparently it was a fuel pressure delivery problem.Not engine related

 

 

[pylon500]

As mentioned earlier, different carbi installations can have different effects.

 

If not using the pre-carb plenum chamber, I think Rotax supplies small springs and tabs to support the weight of the carbi across the manifold rubber.

 

I have seen older carbi rubbers cause leakage as the steel mounting plate moulded within starts to rust.

 

 

[Guest Maj Millard]

I can confirm that the mechanical fuel pump that failed at just over 200 hrs on my friends' Savannah was an AC brand pump. The Pierburg pumps have Pierburg written on the top, the AC one's have a single squarish cut out on the circumference, and a very faint AC on the top. That engine was recieved from Europe as part of the Savannah XL kit. I have a Pierburg on the Lightwing with 700 hrs on it now, with no sign of any dramas. I have bought one of the new style pumps which I carry in the plane, but as long as the Pierburg pump is doing ok, it'll still be along for the ride.............................................................Maj...

 

 

[johnm]

good thread maj

 

good to have some / a summary of the 912 knowledge - thanks

 

................ no 912 bashing yet

 

 

[alf jessup]

I can confirm that the mechanical fuel pump that failed at just over 200 hrs on my friends' Savannah was an AC brand pump. The Pierburg pumps have Pierburg written on the top, the AC one's have a single squarish cut out on the circumference, and a very faint AC on the top. That engine was recieved from Europe as part of the Savannah XL kit. I have a Pierburg on the Lightwing with 700 hrs on it now, with no sign of any dramas. I have bought one of the new style pumps which I carry in the plane, but as long as the Pierburg pump is doing ok, it'll still be along for the ride.............................................................Maj...

Maj,

 

Good thread mate,

 

Just for the record when I bought my 912 trike 6 years back I had it at Floods in Melbourne for a 300hr service, I ask Wal how long the fuel pump would last as mine has a Pierburg on it, his statement was" longer than the engine the, Pierburgs are the best mechanical pump on the market almost bullet proof".

 

So that is quite a statement.

 

Cheers

 

Alf