Light Aircraft down Near Bundaberg

[Oscar]

I suggest we do not have enough information to make truly informed decisions.

 

I would further suggest, that Figure #4 in post 114, shows a previous detached exhaust valve head impacting the head, and bending the adjacent area, witnessed by the oil-blow-by adjacent to it. Figure #5 shows corrosion pitting, which to me suggests that this engine had been sitting idle for quite some time before being installed in the aircraft.

 

I note that the engine had been 'rebuilt' some 400 hours before the accident. AFAIK, Ian Bent owned that aircraft until at least just prior to the demise of CAMit, which was in what - October, 2016? Yet, the engine was 'rebuilt' by the pilot and a friend. The accident happened some 9-10 months at best later; to have racked-up over 400 hours in that time is a remarkable achievement for anything but a FTF aircraft.

 

 

[turboplanner]

I would further suggest, that Figure #4 in post 114, shows a previous detached exhaust valve head impacting the head, and bending the adjacent area, witnessed by the oil-blow-by adjacent to it.

I agree; I didn't scale the photo but the radius looks about the same as this exhaust valve.

 

It's not unusual for mechanics to leave the scar in place; cost saving.

 

 

[ave8rr]

I note that the engine had been 'rebuilt' some 400 hours before the accident. AFAIK, Ian Bent owned that aircraft until at least just prior to the demise of CAMit, which was in what - October, 2016? Yet, the engine was 'rebuilt' by the pilot and a friend. The accident happened some 9-10 months at best later; to have racked-up over 400 hours in that time is a remarkable achievement for anything but a FTF aircraft.

Oscar. The aircraft was not owned by Ian. The owner does alot of flying hence hours flown since overhaul.

 

 

[Csjhay]

Going by the photo, that head has not been on a running engine since the mark was made.

 

Chris

 

 

[Oscar]

Oscar. The aircraft was not owned by Ian. The owner does alot of flying hence hours flown since overhaul.

Aha, thanks. It seemed early on to be accepted that it was Ian's aircraft, glad to have that sorted.

 

 

[turboplanner]

Going by the photo, that head has not been on a running engine since the mark was made.Chris

We are speculating, but I've seen a range of heads ranging from totally pockmarked by shrapnel to clean like the clean section here when the failure has occurred after a few hours.

 

 

[jetjr]

Can anyone identify source of pistons?

 

 

[facthunter]

The more I look at what evidence is there I'm convinced we can't get a full answer. Ring scratching like that is not unusual in a jabiru cylinder. I personally think it's a combination of oil starvation from an excessively effective oil ring and over heating. I also think the 3 piece oil ring material (stainless) is incompatible with the cylinder metal Chromolly steel, posing a critical lubrication situation, compounded by running too hot for the oil film to be maintained.

 

The mark on the head (as if a valve imprint) looks new but it could have been made by something other than a valve. (Gudgeon pin?) about the same size.

 

The rusted and pitted sections are not unusual in left about Jab motors. If a motor with rust is operated the rings can pug up with residue and jamb or break or partial seize the motor. This could weaken a piston which may fail later. This design of piston is already weak between the crown and the skirt. Have a look at one with no oil ring fitted and it's obvious.

 

The top of the piston is one surface of the combustion chamber we have no direct way of measuring it's running temperature. We can get an indication by the carboning of the ring grooves and the underside of the piston. It would have as much effect on detonation as the heads running too hot would. The machined groove in the oil ring area means less heat gets from the crown to the skirt so this factor will make the operating temp of the top of the piston much hotter than other "solid" designs.. The slipper style skirt limits heat travel also. Nev.

 

 

[onetrack]

The ATSB report into the crash is one of the poorest and most incomplete reports I have seen. This was a VH-reg aircraft - where are the copies of the engine build sheet records in the report, to show what was done?

 

The engine S/N is not reported, no one reading the report has any idea of what model or generation of Jab engine it is, or the engines features.

 

There's no mention as to the type of valve lifters, whether it had roller rockers, whether it had the 3/8" or 7/16" through bolts, whether it had suffered damage previously, or what type/brand of pistons were used, either originally or in the rebuild.

 

There's no mention of the reason for the engine rebuild at 403 hours, or whether it had suffered any damage, requiring teardown.

 

The report says "manufactured in February 2010", but this reference still gives the reader no idea of the engine Generation.

 

One has to dig up the June 2016 CASA report on the Jab engine reliability problems, to find the serial number changes as regards the different generations - but even then, no date is apportioned to the engine design changes.

 

https://www.casa.gov.au/file/169776/download?token=BcnNQEBY

 

Then there's the crash report description, "the engine in the aircraft was heavily modified". Once again, where are the written maintenance records outlining what those "heavy modifications" were?

 

A thorough report would include all those records, and report on what they could glean from those records.

 

Nothing is mentioned about piston orientation in the damaged engine, or whether the Jabiru-recommended orientation was followed, in the "heavily modified" rebuild.

 

Interestingly, the engineering report from Jabiru as regards the piston orientation shows a report of piston failure in engine S/N 22J008 - it's possible there have been more, that have not been recorded or reported.

 

http://jabiru.net.au/images/AVDALSR088-1_Piston_Offset.pdf

 

Jabiru state in their 17th Sept 2013 engineering report above, that they use an "automotive piston which has been modified for the application".

 

On the Jabiru website, they state they now use a "Jabiru designed piston produced by a specialist piston manufacturer". No mention of whether that is still just a modified automotive piston.

 

The Jabiru website produces "news articles", such as the introduction of the Generation 4 engine - but every "news article" is undated! Talk about deficient information!

 

Home - Jabiru Aircraft & Engines Australia

 

Then we have the thorough CASA engineering report of May 2016, relaxing the previous restrictions on Jabiru engine operation.

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwi2jdLhgJfWAhWJTbwKHQs_BcsQFghLMAM&url=https://www.casa.gov.au/file/169776/download?token=BcnNQEBY&usg=AFQjCNEsD2r-ByBszbAA6Usr0BZf_yWOAQ

 

This extensive report lists only one piston failure in Jabiru engines, and also lists the "new design" piston with machined recesses for the valves, as being introduced in September 2013 - but doesn't state whether that introduction coincided with any new Generation engine, or whether it was introduced as a modification within the current Generation engines.

 

The move to machined recesses in the piston heads doesn't really address what the actual problem is, that is causing the stuck valves, and seems to me like the piston redesign is just a defensive move, rather than a proactive move to find out the precise reason for valves sticking, and address the cause or causes.

 

Re the head damage in the photo in the crash report, I would suggest that damage was caused by a piston circlip, after being freed by piston collapse, being driven into the head surface.

 

 

[turboplanner]

That's all very familiar to us because we had several years of open discussion down to the last minute detail over and over again whereas I think an investigator would be lucky to be able to extract all that.

 

 

[jetjr]

Why would you take a heavily modified engine back to original maker and expect independant analysis?

 

 

[geoffreywh]

I would expect the manufacturer to go thru' the engine with a fine tooth comb to clear his name of any fault, and to lay any blame at the door of the modifier

 

 

[jetjr]

They laid blame at modifier before the aircraft was removed from paddock

 

 

[Oscar]

I would expect the manufacturer to go thru' the engine with a fine tooth comb to clear his name of any fault, and to lay any blame at the door of the modifier

With respect - on ALL of the evidence, could you seriously expect Jabiru to accept blame? That would be like requiring a surgeon to accept blame for the death of a former patient on whom he had operated, when several yards of Bunnings Medical Supplies garden hose and a bunch of plumbing fittings were found inside and the patient had admitted he did 'Home Surgery'.