Two Engines, One Control System: Impossible or Inevitable?

[wolram]

http://news.uk.msn.com/Article.aspx?cp-documentid=7279188

Surly both engines do not share a single control system.

 

[mgb_phys]

The suggestions on the aviation forums are that engine icing could have slowed both engines to the point that the generators dropped out.

 

[wolram]

The suggestions on the aviation forums are that engine icing could have slowed both engines to the point that the generators dropped out.

Would this be a type problem or general or may be a million to one set of circumstances?

 

[mgb_phys]

I think blade icing is a problem in large diameter engines like the 777 and A380
as the engine gets bigger the bleed air to heat the blades is less effective.
The suggestion is that the engines were icing but were running at low power - on descent so it didn't matter - when the pilot turned up the power they both slowed quickly.
I suppose you can't carry enough battery power to run the controls without the generators but it is worrying on something like the 787 where the surfaces are powered by electric actuators.

The other suggestion is that it ran out of fuel, it shouldn't have and would have given a warning - unless the plane had been improperly filled and the gauges/fuel monitors had failed.

 

[FredGarvin]

The suggestions on the aviation forums are that engine icing could have slowed both engines to the point that the generators dropped out.

No way. Generators on large engines are driven by large transmissions called CSDs (constant speed drives). I have a very hard time believing that there would be nacelle icing that was so bad to ice up a generator to the point of not working. The thermal soakback from the engine alone should be enough to keep it happy, not to mention the relatively hot cooling oil circulating through it. I would need a lot more data to convince me of that one.

Icing, in general, is a tough one to accept. When we certify an engine, we go down to Eglin AFB and put it in their icing facility. The engine has to perform under severe icing conditions. The same is for the big boys. Again, there would have to be an normous amount of icing to do what is being described.

The idea that both FADEC systems went bad is pretty remote.

The fuel idea is the simplest and most direct one that is easiest to accept at this point.

 

[russ_watters]

Would this be a type problem or general or may be a million to one set of circumstances?

Whatever the problem ends up being, it is both. Planes are required to have reliability that exceeds million-to-one failure odds.

 

[mgb_phys]

The engine has to perform under severe icing conditions. The same is for the big boys.

Yes, having seen the conditions they are tested under in Canada - it's hard to believe a foggy morning in London could kill both engines.

The idea that both FADEC systems went bad is pretty remote.

Is this the same Boeing that does FADEC on the RAF Chinooks?

The fuel idea is the simplest and most direct one that is easiest to accept at this point.

There was a suggestion that ice forming in the bottom of the tanks is a problem on the 777, I don't know if this could happen in such a way as to make the fuel management system think it was OK but still starve the engines.

 

[Astronuc]

I wish some organization besides Wikipedia would post the details, but - http://en.wikipedia.org/wiki/British_Airways_Flight_38

Does icing of the engines or fuel system seem credible/plausible based on the plane and location? I imagine that similar aircraft were flying similar or more onerous conditions. Beijing to London is a polar round IIRC, and I've flown similarly northern routes from Tokyo/Osaka to NY(EWR/JFK)/SFO. The route and the conditions are not that unique, and the 777 is a more advanced aircraft.


Some more information.

http://aviation-safety.net/database/record.php?id=20080117-0

http://www.aaib.dft.gov.uk/latest_news/accident__heathrow_17_january_2008___initial_report.cfm


Interestingly, there was a problem with the 777 in Australia.
http://www.airlinesafety.com/faq/777DataFailure.htm

On August 1, 2005, a Boeing 777-200, which had departed from Perth, received an EICAS (Engine Indication and Crew Alerting System) warning of low airspeed, as the plane was climbing through FL (flight level) 380. Simultaneously, the aircraft’s slip/skid indication moved full right, on the PFD (Primary Flight Display). The PFD speed tape also displayed contradictory information: that the plane was approaching both the high speed limit and the low speed (stall) limit. The aircraft, still connected to the autopilot, pitched up and climbed to approximately FL410 as the airspeed decreased from 270 kts to 158 kts. The stall warning devices also activated.

I wonder if this failure had any commonality with the BA038 problem.

 

[FredGarvin]

Is this the same Boeing that does FADEC on the RAF Chinooks?

Hmmm. That's a curious question. To answer, the FADEC is produced by the engine manufacturer, not the airframer. So th answer would be no. It would be developed and produced by GE whereas the Chinook (genuflect when you say that) uses Honeywell-Lycoming T-55's. Has there been any issues in the UK with their aircraft? I try to keep an ear to the ground when it comes to Chinook issues and I haven't heard anything.

There was a suggestion that ice forming in the bottom of the tanks is a problem on the 777, I don't know if this could happen in such a way as to make the fuel management system think it was OK but still starve the engines.

Is that on the inside of the tanks? Anything is possible, that's for sure.

 

[mgb_phys]

There was a crash about 10years ago of an RAF Chinook. The craft had been updated with new FADEC, the crash was blamed on pilot error (many felt unfairly) and it was felt the technical problems were covered up - apparently the entire model was grounded and still haven't been returned to service.

The helicopter was on a secret mission carrying inteligence officers/agents and special forces from Northern Ireland so there was a general air of cover-up.

http://en.wikipedia.org/wiki/1994_Scotland_RAF_Chinook_crash

 

[FredGarvin]

I remember that crash. I jut read a blurb in my aerospace testing magazine that the MoD has just allowed an upgrade program to go to the HC3. I had never heard anything about the FADEC problems though, just the overall control systems. It's strange because there are so many operational Chinooks around the world. I wonder if there is a difference in the types of controls. Thanks for the link.

 

[drankin]

I work with a man (one of our consultants) who was involved in the development of the 777 landing gear. He believes they simply ran out of fuel on final approach. The plane was coming from China, so it's as plausible as any specualations at this point. The reason we wouldn't hear about that right away is it that would be an embarassing admission. It would certainly explain sudden engine failure in BOTH engines at the same time.

Also, he said the landing gear failed correctly. From the pictures of the landing gear that separated you can see where one of the enormous titanium supports sheared completely. Amazing!

 

[DrClapeyron]

Sounds like a loss of fuel pressure due to ice cover. Someone removed an ice shield or heat shield and never placed it back in.