Airborne exhaust cracking (IMPORTANT NOTICE)

[Bluey]

Some of you may have received an email recently regarding a defect notice issued by the HGFA about a possible exhaust component problem. The email described a number of incidence of the question mark shaped exhausts cracking on an XT912. I have had 5 cracked exhaust pipes including one catastrophic inflight fracture where the pipe cracked in two resulting in an emergency landing. After extensive discussions with right people at airborne, it has been discovered that the process of making changes to the exhaust needs to be clarified. Many airborne operators I have spoken to have mistakingly followed incorrect procedure for making adjustments to the exhaust. The process described involves attaching the exhaust components to the engine and attaching the springs before tightening any of the nuts that hold the exhaust components to the engine. This is an incorrect process that has resulted in 5 exhaust pipe failures on two seperate trikes in the last 12 months. Two failed exhaust compnents were virtually brand new. As a result of the failures of these new compnents I was led to believe that there might exist a quality control problem with the latest batch of manufactured parts.

 

I have anecdotal evidence that others have experienced problems with exhaust cracking and or failure. I can list at least one individual that has had two failures. One involving cracking and one catastrophic failure resulting in an emergency landing. In all cases that I have experienced problems, they all occured after the exhaust was worked on. On one trike that was purchased recently, the previous owner was asked to repair some wear to exhaust lugs. The previous owner removed the affected exhaust components and then re-attached the exhaust using the above mentioned method. 15 hours later I had two cracked question mark pipes. My first cracked exhaust about 12 months ago occured shortly after an EGT probe was replaced where the exhaust part was removed to make the repair easier. Recent failures of new parts all occured after exhaust components were removed.

 

It appears quite clear that any tampering with the exhaust that involves the adjustment of the nuts holding the exhaust to the engine induces stress in exhaust components. In order to ensure exhaust longevity all exhaust stress needs to be elliminated at time of installation. This kind of exhaust stress is the major cause of premature failure in the question mark pipes.

 

The correct procedure for elliminating exhaust stress is to align the exhaust the following way whenever any exhaust parts are separated from the rest of the exhaust:

 

1. loosely attach the exhaust components to the engine.

 

2. Slowly tighten the nuts to the question mark shaped pipes constantly checking that the mufler can be easily moved with the pipes in place. The mufler should be rotated 180 degrees to ensure it is properly aligned in both directions. When the nuts are properly tightened the mufler should be able to be removed from the pipes without any stress on either of the pipes.

 

3. Do the same with the two horizontal pipes under the engine with the muffler in place. These pipes are not as critical as the two shorter pipes since they are longer and have a greater degree of flexibility.

 

4. Finally, once all the pipes are aligned and tightened in place, attach the springs.

 

Note: Make sure you use antiseize grease on all the joints.

 

This method needs to be followed whenever any of the nuts holding exhaust components are either loosened or tightened as their adjustment will cause stress (especially problematic for the short pipes). For instance the short pipes will move horizontally either left or right when either nut is adjusted resulting in the build up of stress on each of the short pipes.

 

It is no surprise that many are not aware of the correct procedure for working on the exhaust as very few have ever had to touched it. If you do however, beware of the consequences of doing it the wrong way.

 

I believe it is in Airbornes best interest to include written instructions whenever supplying new exhaust components to their customers. They are yet to do this and in my opinion should bare some of the responsibilty for any problems caused when the new parts fail prematurely. I have checked the XT912 maintainance manual and no mention of any procedure is included. It does however state that you should call them to arrange for any new exhaust parts you might need to order.

 

Finally, it is important to realise that the process of changing exhaust springs will not require a full exhaust alignment as none of the nuts are adjusted for this process.

 

Bluey.

 

 

[alf jessup]

827hrs Bluey and no cracking as yet, i have not removed the muffler or pipes since owning the trike 5 years, I do occasionally lube the joints with this silver colored spray on stuff, can't remember the name of it for the life of me.

 

Alf

 

 

[Bluey]

It appears that if you leave it alone you'll get really good life out of it. However, the moment you touch it you'll be in trouble. I'm surprised the procedure for working on it hasn't been better publicised.

 

 

[alf jessup]

It appears that if you leave it alone you'll get really good life out of it. However, the moment you touch it you'll be in trouble. I'm surprised the procedure for working on it hasn't been better publicised.

Seems the case Bluey,

 

But then again a mate of mine who bought his trike at 19hrs and never fiddled with his exhaust had the 2 ? pipes crack on his at about 150 hrs.

 

It may seem that some installations from the factory may not of been set up right from the first place.

 

I have the theory if it aint broke don't fiddle with it.

 

Cheers

 

Alf

 

 

[Bluey]

I agree with you Alf especially in the case of the exhaust. How did your mate fix the problem? Did he by any chance replace the pipes with new ones from airborne?

 

On a side note, how's your gearbox? Have you had it inspected (600hr inspection)?

 

Bluey

 

 

[Bluey]

Another point I forgot to mention is that airborne claim that they have only ever sold 7 exhaust pipes to their customers in more than 400 manufactured trikes. I believe the incidence of cracking is more wide spread than they are aware of because most people don't go to them for the repairs. Of the few incidents I know of that have occurred to other owners, the exhaust parts were repaired by reputable exhaust repairers. How well these repairs are standing up to the test of time is unknown to me at this time.

 

Bluey.

 

 

[alf jessup]

Na mate he got the pipes tig welded up, one cracked again and was rewelded, he fiddled with the alignment and has had no trouble since.

 

On the gearbox, na havent touched it mate, check for side play each time i preflight it and pull the prop through listening for anything not sounding right and its as good as the day i got it.

 

When i first bought the trike at 287 hrs i took it to a dealer and got a service and carb balance ect and asked them a few questions about the 912 and the 1500hr TBO.

 

Basically got looked at in a funny way and was told that these 912 motors have done some incredible hrs in other aircraft and never been touched.

 

I have replaced the diaphrams in the carbs and needles and intake rubbers also at the recommended hrs Rotax states and had been told why bother but i did it anyway.

 

I have a mate who was a BMW bike mechanic who now does my carb balancing as the carbs 912's run are the same as the bm's were during his time at BMW.

 

I am regular in my servicing, oil and filter every 50hrs change the hang bolt every 50, plugs every 150 clean and re oil my air filters every 200.

 

Cheers

 

Alf

 

 

[alf jessup]

On the welding side of it, it is far better to get them tig welded rather than mig, as mig is a cold start weld which the cracks will appear usually at the start of where it was first welded.

 

 

[Bluey]

yes, I have been told that tig welding is the way to go with any welding on these exhausts. Shane at airborne has asked permission to contact any other owners that have had exhausts crack. Any chance of getting contact details for your mate so Shane can have a chat to him about it. As you can imagine it is in their best interest to find out if there is an issue that needs fixing? If you can't do it then don't lose any sleep over it.

 

Bluey

 

 

[alf jessup]

I'll ask him next time I speak to him if he is cosha with that, He is currently going through a really tough time with his wife and her illness

 

 

[Bluey]

Sorry to hear about that.

 

 

[Bluey]

Airborne are asking for A survey from trike owners who have ever had any problems with their exhausts. If anyone has any reliable information of exhaust cracking or breaking that they know of please post it here. Names are not required just reliable information. This is a rather important survey as the anecdotal evidence seems to suggest it occurs more than airborne are aware. They at this point in time are confident the exhaust components they are currently producing are perfectly adequate, where as I had a new question mark tube show signs of cracking again after just 6.5 hours of service. This is despite the fact I removed the springs and ensured the muffler could be slid away from the pipes with ease before i flew yesterday. After 1.3 hours of flight a crack was starting to develop in the same part I just replaced! Airborne are insisting that there must be large stresses on the exhaust somewhere. I and others who have inspected it don't see it. My question is why the same part all the time? This is now four broken new pipes, three on one trike and one on another. Any ideas?

 

Bluey