[ldbtx]

This is from AVWeb Flash for today, regarding the uncontained engine failure on a BA flight departing KLAS. I know that some of y'all have worked on these engines. I'd be interested in any comments or experiences.

"Inspections of older GE engines on airliners around the world could begin in the coming weeks as investigators learn more about the uncontained engine failure that started a fire on a British Airways jet one month ago in Las Vegas. In an update from the NTSB this week, investigators found that a disk in the high-pressure compressor (HPC) in the 777’s left GE90 engine fractured during takeoff roll, propelling pieces into the engine case and cowling. “GE is performing high-priority, focused inspections of HPC hardware from other GE90 engines,” the NTSB said. According to a Seattle Times report, GE is examining similar compressors that have been in storage to find clues that would aid field inspections. About 400 similar engines are in service, the report said.

The British Airways jet aborted its takeoff at McCarran International Airport on Sept. 8 when the engine caught fire. The 158 passengers and 13 crew evacuated the aircraft using emergency slides. A GE spokesman told the Seattle Times the engine had been in service since 1997, while the broken disk in the compressor was built in 1995, when the first GE90s were made. This was the first case of an uncontained engine failure in this model engine; similar incidents with different GE engines have been documented, according to the report."

[Cricket]

As far as I know there are no welded parts in a turbine itself. Blades are assembled with the "tree" connection. There are welds in the tubing flanges etc. but they cannot cause such a failure. Usually the main disk is forged from Ti and is prone to fatigue fractures and Ti defects. That kind of failure had happened before.

[ex framie]

It could be any one of several causes ranging from a lubrication failure to a microscopic metallurgical flaw.
You really cant tell until they finalize the incident report.
However a disc that weighs a couple of hundred pounds spinning between 10,000 and 20,000 rpm in a very hot enviroment is exposed to an extreme number of forces.
I'm actually surprised it doesnt happen more often.

[Otto Nobedder]

What scares me is the possibility of a new failure mode being discovered after "time in service".

Austinitic stainless steels were in service many years before "Stress Corrosion Cracking" and "Pit Corrosion" were discovered. These phenomena now put food on my table. I don't find it on anything much younger than 20 years in service in weldments, and 40 years in non-welded areas.

Could there be some as-yet undiscovered failure mode for Ti parts, either through stress accumulated over time, or chemical interaction from fuel additives, atmospheric/ozone effects, or some combination of these?

I'll be very interested in the final analysis.

Steve S

[ex framie]

Total failuers are rare thankfully due to the inspection progam and lifeing of engine parts.
Still its not easy doing and interpreting inspects throught a borescope with a limited field of view and depth perception. Our moto in the military was when in doubt pull it out for an in depth look ( money no object + I was probably going on the test flight).
The civil side have a slightly different view and drastically different operating environment, they do have and adhere to a ridgid maintenance regimen but the intervals are generally longer and lets face it you could count on 1 hand the number of dramatic engine failures over the last 5 years over how many millions of flights, while disturbing when they happen the risk is infantisimal.
Steve,
The main cause of failures is cyclic stress, hot/cold cycles, operating rpm, overheating or mechanical damage which acts as a stress raiser. Rarely it is a missed micro flaw at the intergranular level which when exposed to the above operating enviroment eventually make themselves known, sometimes spectacular enough to make the six oclock news.

[noddybrian]

Although rare - this type of failure has been known about for a long time - I believe the Sioux City crash was caused by it & the conclusion as I remember it was defect at manufacture that had escaped testing throughout the engines life - so maybe it's time for a new test method or replacement after a set number of hours ? but with the costs of running planes rising more than air fares I guess there is still a limit of money available for safety against risk ? there will always be a conflict of interest - at least no one has run one out of fuel lately !

[OzFlo]

Lets not confuse turbines and compressors. The report said that it was a failure of one of the high pressure compressor discs. Most of the time when a compressor stage is damaged in operation it is due to ingestion of a foreign object - be it a bird, or rock or other debris sucked up of the runway/taxiway. There have been instances where individual compressor blades have been liberated from their discs but it's rare and as for a compressor disc failing; that is extremely rare! Compressor stages have a much easier life than do turbine stages.

The role of the turbine is to extract as much energy out of the hot exhaust gas as possible in order to drive the fan.

The Sioux City DC-10 accident was the result of a turbine disc in the number 2 engine letting go and severing critical primary flight control hydraulic lines in the tail of the aircraft making the aircraft uncontrollable. The flight crew in that particular case did a tremendous job to use the thrust of the two good engines to regain partial control of the aircraft and minimise the number of casualties. Had that same failure occurred in either the number 1 or number 3 engine it is more than likely that the aircraft could have landed safely.

[noddybrian]

Thanks for the clarification - I did'nt take much notice of the news report on the BA flight so it just seemed similar to the DC-10 - some crashes like that stick in the mind for many years especially as you say the flight crew did the nearly impossible to get it down at an airport so that they had a chance - I remember a program that showed the circles of it's flight path while trying to keep it level & close in on the runway & the subsequent search for the missing engine parts quite amazing - the Gimli glider also sticks in the mind - part for the fact they ran one out of fuel & part the fact the 767's flight data was used on a simulator & no other pilot managed to keep control let alone get close to putting it down - sad thing is it's unlikely younger pilots will achieve experience to cope with in flight problems as the computers do all the flying for them so the slightest computer glitch can cause a crash such as the airbus piton tube freeze up.