Airbus A380 Mid-air Engine Failure

[Mize]

Ostensibly yes, wing damage could bring the plane down. However, it did still land safely. There is obviously a question as to how close the aircraft came to dangerous failure, but so far there is insufficient evidence to suggest this.

Thanks for stating known facts

Catastrophic wing damage is unlikely, but significant wing damage resulting in fuel loss far from any airport (say half way between Tokyo and Los Angeles) is a dire situation. This is why containment is so important. I spent 14 years in airworthiness assurance engineering and uncontainable rotorburst is by far the most dangerous mechanical failure possible next to catastrophic frame failure which is unheard of on a modern plane.

 

[Mize]

The spoilers on the wing of the blown engine didn't deploy when landing.
Control to the outer engine on the wing with the blown engine was lost and started running at climb throttle levels (valves default to open when control is lost.) The engine was drenched by firefighters after the plane had landed.

People are speculating that it was a failure in the rotor, not a blade failure. The engine is designed to retard blades. The rotor can't be stopped, too high mass.

Cheers

Ah, so it was rotorburst. Totally unacceptable on an engine that new. That's a clear manufacturing defect in machining or heat treating that should have been caught. Damn things can rip through the entire fuselage.

 

[KimB]

Ah, so it was rotorburst. Totally unacceptable on an engine that new. That's a clear manufacturing defect in machining or heat treating that should have been caught. Damn things can rip through the entire fuselage.

Well, Gubbi was reporting on suspicions. However, I'd be curious to know what rotor burst is. I'm having a hard time finding anything useful about it on Google (lots of technical documentation talking about dealing with them in various forms, but no simple explanation I could find in a quick search).

 

[Mize]

Well, Gubbi was reporting on suspicions. However, I'd be curious to know what rotor burst is. I'm having a hard time finding anything useful about it on Google (lots of technical documentation talking about dealing with them in various forms, but no simple explanation I could find in a quick search).

Seriously?
Google "rotor burst" and I think you'll have ample reading.

The rotor is the central spinning hub of the turbine to which the turbine blades are mounted.

 

[KimB]

Seriously?
Google "rotor burst" and I think you'll have ample reading.

Yeah, nothing that I could easily get into.

The rotor is the central spinning hub of the turbine to which the turbine blades are mounted.

That's the main part I was missing. I had a hard time finding even that much about what a rotor is the context of an aircraft engine. So you're saying that the rotor itself breaks in a rotor burst? Does it tend to split down the length of the rotor? Or tear itself in a corkscrew fashion? Does it break into a relatively small number of pieces? Or does it start with some sort of small break and just shatter into thousands of pieces?

 

[aaronspink]

Not terribly worrying. From what I understand, these aircraft are designed such that the failure of one engine is insufficient to bring the plane down. The simultaneous failure of both engines is exceedingly unlikely.

This assumes contained failures. Part of the reason there is some concern about this incident is because it was an un-contained failure.

 

[Mize]

Yeah, nothing that I could easily get into.


That's the main part I was missing. I had a hard time finding even that much about what a rotor is the context of an aircraft engine. So you're saying that the rotor itself breaks in a rotor burst? Does it tend to split down the length of the rotor? Or tear itself in a corkscrew fashion? Does it break into a relatively small number of pieces? Or does it start with some sort of small break and just shatter into thousands of pieces?

They can break in many different ways depending upon the material, heat treating, alloy, etc. The very large rotors used in power generation often split down the middle. In all cases it's your basic coalescence of vacancies -> crack -> crack growth with poor pinning -> catastrophic failure.

For this to fail so early in it's life it is a substantial material failure. Alloying or heat treating was defective.

There are many different efforts to prevent and contain rotor failures - both in jet engines and in gas turbine power generators. Containment includes stopping the pieces of the failed rotor and/or ensuring the fly in harmless directions.

The wing and/or fuselage are the two worst directions.

 

[KimB]

They can break in many different ways depending upon the material, heat treating, alloy, etc. The very large rotors used in power generation often split down the middle. In all cases it's your basic coalescence of vacancies -> crack -> crack growth with poor pinning -> catastrophic failure.

For this to fail so early in it's life it is a substantial material failure. Alloying or heat treating was defective.

Interesting. That would likely mean that a large fraction of the engines in A380's would likely need to be overhauled. If this is the case, then it would be a massive hit for Airbus.

 

[Mize]

Interesting. That would likely mean that a large fraction of the engines in A380's would likely need to be overhauled. If this is the case, then it would be a massive hit for Airbus.

Massive hit for Rolls Royce too as Airbus has a GE option.
As I stated earlier, Rolls Royce makes great engines, but some of their heat treating, I've been told, is archaic. I've been told they still use pack carburizing (a method for hardening steels that diffuses carbon into the steel by packing it in ashes at temperature) whereas most people have been doing gas carburzing since WWII and controlled gas carburizing since the 80s.

 

[Grall]

next to catastrophic frame failure which is unheard of on a modern plane.

There was that one jumbo where the rear pressure bulkhead gave way after a faulty repair job and escaped air blew out the entire rudder. ...Crash boom. I forget when it happened, must have been sometime in the 80s. I guess that qualifies as "modern plane", although it involves human error of course. Probably not what you were thinking of.

 

[Mize]

Indeed:

The final investigation report found that the accident was the result of metal fatigue caused by inadequate maintenance after a previous incident. The report finds that on 7 February 1980, the accident aircraft suffered damage from a tailstrike accident while landing in Hong Kong.[19] The aircraft was then ferried back to Taiwan on the same day de-pressurized, and a temporary repair done the day after. A permanent repair was conducted by a team from China Airlines from 23 May through 26 May 1980. However, the permanent repair of the tail strike was not carried out in accordance with the Boeing Structural Repair Manual (SRM). The area of damaged skin in Section 46 was not removed (trimmed) and the repair doubler plate that was supposed to cover in excess of 30% of the damaged area did not extend beyond the entire damaged area enough to restore the overall structural strength. Consequently, after repeated cycles of depressurization and pressurization during flight, the weakened hull gradually started to crack and finally broke open in mid-flight on 25 May 2002, exactly 22 years to the day after the faulty repair was made upon the damaged tail. An explosive decompression of the aircraft occurred once the crack opened up, causing the complete disintegration of the aircraft in mid-air.[1] This was not the first time, though, that an aircraft had crashed because of a faulty repair following a tailstrike. On 12 August 1985 (17 years earlier), Japan Airlines Flight 123 crashed after losing its tail and hydraulic systems. That crash had been attributed to a faulty repair to the rear pressure bulkhead, which had been damaged in 1978 in a tailstrike incident.

This is amazingly stupid. Doublers work. You've all seen them as you enter any older plan you will see doublers above the right side of the entry doors. To put a doubler on that doesn't extend beyond the damage regions is just idiotic. A properly installed doubler is as strong as the skin it replaces.

Anyway, it still wasn't frame failure - it was explosive decompression (skin failure) at 35,000 ft. Not survivable.

"if we should experience a sudden loss of cabin pressure [at 35,000 feet] forget the masks and kiss your ass goodbye"

 

[aaronspink]

Interesting. That would likely mean that a large fraction of the engines in A380's would likely need to be overhauled. If this is the case, then it would be a massive hit for Airbus.

There is speculation that the failure is related to a maintenance notice that was put out by the FAA as a result of an un-contained failure on the Trent 1000 in testing with the 787. The teardown of the 1000 revealed that their was faster than expected wear down around the rotor bearing of the intermediate pressure turbines. The maintenance notice basically changed the maintenance/inspection intervals for the engine based on the wear level and width of the remaining material.

If the issue is the same and the updated maintenance scheduled were being followed by QF, then it is likely that the notice will once again be updated with an even more accelerated maintenance schedule which may or may not have significant financial impact. At this point though, it is safe to assume that those who went with the Engine Alliance solution for the 380 are probably giving themselves high fives right about now.

The main impact of this is if it takes a while for RR to come up with a permanent solution which doesn't require an accelerated maintenance schedule wrt the Trent 1000 and the 787. The 787 design is such that it is the simplest plain designed so far for engine swapping. The original design specs basically have it as one week operation. Remove RR pylon and replace with GE pylon. Done. This gives purchasers some significant leverage in switching their engines late in the order process. Previous bleed designs were much more integrated into the airframe and switch engine manufacturers was all but impossible. Considering that RR has sold a significant number of 1Ks for the 787, if the airlines get nervous and switch, it could have significant financial impact.

 

[aaronspink]

Indeed:
Anyway, it still wasn't frame failure - it was explosive decompression (skin failure) at 35,000 ft. Not survivable.

Wasn't there an issue with one of the Airbus model (I want to say 300 or 310) with structural failure due to fatigue of the composite tail fin/cone?

 

[pcchen]

Wasn't there an issue with one of the Airbus model (I want to say 300 or 310) with structural failure due to fatigue of the composite tail fin/cone?

Do you mean the AA Flight 587 crash? The tail broke off and the airplane crashed, but the investigation pointed to incorrect rudder usage (and probably also bad rudder design) which created excess stress on the tail fin.

 

[aaronspink]

Do you mean the AA Flight 587 crash? The tail broke off and the airplane crashed, but the investigation pointed to incorrect rudder usage (and probably also bad rudder design) which created excess stress on the tail fin.

Yep, that's the one. And quite honestly, I'd side with the pilots association in this. The rudder was poorly designed.

 

[Grall]

"if we should experience a sudden loss of cabin pressure [at 35,000 feet] forget the masks and kiss your ass goodbye"

...Unless it's a Hollywood movie of course, in which case 2-3 people will fly out of the hole in the side of the aircraft and wind and flying paper will whirl around in the cabin while the hero and the badguy slug it out for two minutes straight while the plane dives with a stuka bomber propeller-whine sound effect added for effect, then the badguy will fall out of the hole, the plane levels out, and all the papers will stop whirling as if by magic. Roll credits; the end.

 

[Gubbi]

So you're saying that the rotor itself breaks in a rotor burst? Does it tend to split down the length of the rotor? Or tear itself in a corkscrew fashion? Does it break into a relatively small number of pieces? Or does it start with some sort of small break and just shatter into thousands of pieces?

The fan, compressor and turbine blades are attached to rings, which are driven by the shaft. The rotor is really the assembly of shaft and rings.

In this case, the failure appears to be one of the rings.

Cheers

 

[Mize]

Wasn't there an issue with one of the Airbus model (I want to say 300 or 310) with structural failure due to fatigue of the composite tail fin/cone?

That was an improper repair of the composite tail over Long Island. Definitely closer to what I was saying though as it was only "improper" because there is no solid database for composite repairs. They mainly chocked it up to wash turbulence though, didn't they? I'd have to go look it up.

[Edit] pcchen's right - they said the wash turbulence resulted in rapid oscillation of the rudder that overstressed the tail or something like that.

 

[Sxotty]

Anyway, it still wasn't frame failure - it was explosive decompression (skin failure) at 35,000 ft. Not survivable.

"if we should experience a sudden loss of cabin pressure [at 35,000 feet] forget the masks and kiss your ass goodbye"

Why is that? The pressure change? Does everyone get the bends? I mean 0.21 atm from 0.5 atm is what it would be right? Otherwise people can live on everest at 30k so it seems that would be long enough to do something like lower the altitude etc.

 

[Mize]

Why is that? The pressure change? Does everyone get the bends? I mean 0.21 atm from 0.5 atm is what it would be right? Otherwise people can live on everest at 30k so it seems that would be long enough to do something like lower the altitude etc.

1. People on everest are wearing slightly warmer clothing
2. People on everest have O2
3. People on everest aren't falling out of the sky surrounded by the shrapnel like remains of an aircraft that just disintegrated around them


3. is obviously the real kicker.

Now certainly you can imagine a very small skin puncture that could be survivable. The problem is that the skin is meant to handle the tensional, hydrostatic stress as one system. puncture even a small hole and you get a localize stress concentrator (from escaping air) that will tear the skin like a hot knife through butter. Lose a bit of that skin and now your fully depressurized but you have an aerodynamic anomaly in the airframe that might be survivable at low speeds, but you're going 700 mph so it starts to rip more skin and frame ribs and the plane literally breaks to pieces.

A situation like Aloha 243 is certainly possible but unlikely (and that 737 was only at 24,000 feet).