BA 777 crash at heathrow

reply to post by Zaphod58
Zap you are the closest I have to an expert, I tried asking this in pprune and I was booted out faster than a B2 pilot can eject.

All the theories I have read so far 99% have dealt with a constant obstruction to the fuel flow as the primary cause. However the only anomaly AAIB has come up with is cavitation in the High Pressure fuel
pumps (mech driven) on the engines.

My question and theory, Will cavitation once started by a very temporary
fuel obstruction, continue limiting fuel pressure to the FMU (Fuel Metering Unit) unless specific measures are used to correct the cavitation??
Assuming the throttles are not closed to allow cavitation to stop.

Or (as everyone with Pilot in their resume except one) seems to think
the cavitation will stop once the fuel from the low pressure pumps flows
again!!!

ie. Cavitation is so strong they are using it for Nuclear Fusion experiments of Deuterium Doped Acetone, If the Throttles are opening in the FMU (First Auto Pilot then real Pilots) causing an even lower pressure on the High Pressure side of the HP pumps causing even more cavitation Is this the primary cause of low engine output thrust?? Does it seem more likely now that AAIB is scratching their heads?


PS anyone experienced with cavitation may reply, I also know that won't stop you:-)

From my understanding of fuel pumps, once cavitation starts, it can stop on its own, BUT, you have damaged the fuel pump at that point and it may not pump as efficiently as it was before the cavitation started. Cavitation is caused when SOMETHING creates bubbles in the fuel, or blocks the fuel from getting to the pump. Once you get normal flow back to the pump the cavitation SHOULD stop. In the cockpit you may not even be aware that it was happening.

Keep in mind that I wasn't a fuel guy, but that's how *I* understand it from talking to some of the fuel guys I used to know and keeping up with stuff in books.

Now THIS is interesting. AA299, a Boeing 777 flying from Miami to Los Angeles, suffered a throttle hang for 10-15 seconds in the left engine. The engine remained at descent idle, when the autothrottle commanded an increase in thrust. It hung at that setting for 10-15 seconds while the right engine spooled up. Then it finally began responding to commands. All American aircraft use the Trent 800 engines used by the BA777 that crashed recently.

[edit on 2/29/2008 by Zaphod58]

SUBJECT: 777-300ER/777-200LR Failure to Scavenge Fuel

/A/ Service Related Problem 777-SRP-28-0118
/B/ Fleet Team Digest Article 777-FTD-28-07002

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

SUMMARY:
Note: This message contains important information relevant to flight operations and airplane dispatch, please distribute accordingly.

Several 777-300ER operators have reported intermittent occurrences of airplanes landing with as much as 2200 lbs/1000kgs/300 gallons of fuel in the center tank. Boeing theorizes that this is an indication that the fuel scavenge system has malfunctioned. A failure such as this of the fuel scavenge system reduces the range of the airplane and could potentially lead to fuel exhaustion in the event additional failures occur which require use of all planned reserve fuel. To address this concern, Boeing recommends that 777-300ER and 777-200LR operators review their fuel reserve policy to ensure adequate reserves exist for each mission.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

DESCRIPTION:

The scavenge system is designed to transfer fuel from low areas of the center wing tank to the main tanks after the override pumps are shut off. Scavenging this additional fuel from the center tank increases the fuel available for engine use. The 777-300ER and 777-200LR airplanes have incorporated scavenge system design changes intended to increase the amount of fuel scavenged and reduce the amount of trapped unusable fuel in the center tank to approximately 3 gallons. These changes included relocating the fuel scavenge inlet further inboard, while the water scavenge inlet location remained unchanged. Additionally, the fuel scavenge outlet and float valve were moved further outboard to allow fuel scavenge to be initiated earlier in flight.

Several 777 -300ER operators have reported intermittent occurrences of airplanes landing with as much as 2200 lbs/1000kgs/300 gallons of fuel in the center tank. Boeing theorizes that this is an indication that the fuel scavenge system has malfunctioned. These instances have only occurred on long routes originating from colder climates and have led to the conclusion that an excessive amount of water is entering the fuel scavenge system and is freezing during scavenge operations. Because the water scavenge inlet was not co-located with the fuel scavenge inlets it is more likely for water to be ingested in the scavenge system. Additionally, as the outlet float valve location is further outboard in the main tank than previous, the scavenged center tank fuel has more exposure to the cold soaked main fuel tank prior to reaching the scavenge discharge. Indications are that the water in the scavenge system is freezing prior to discharging in the main tank. Frozen water (or ic!
e) in the scavenge system could result in a low rate of scavenge or no fuel scavenge.

Failure of the fuel scavenge system could result in airplanes landing with as much as 2200 lbs (1000 kgs) of fuel in the center tank. During mission planning and dispatch, this fuel in the center tank was considered usable fuel. However, failure of the fuel scavenge system in flight renders this 2200 lbs (1000 kgs) of fuel as unusable. There is no indication to the flight crew that the scavenge system has failed and the fuel is unusable. Failure of the fuel scavenge system essentially reduces the range of the airplane and could potentially lead to fuel exhaustion in the event additional failures occur which require the use of all planned fuel reserves.

Boeing review has determined that the failure to completely scavenge the center tank is the result of system configuration changes unique to the 777-300ER and 777-200LR airplanes. This issue has been placed in our Service Related Problem (SRP) process for resolution and is the subject of the REF /B/ Fleet Team Digest article.


DESIRED ACTION
===============
Boeing recognizes each operator establishes its own fuel reserve policy. Some operators choose to add additional conservatism to existing regulatory fuel reserve requirements. In addition, we note that not all routes and/or operators have shown a susceptibility to this condition. This may be because of environmental conditions, individual airline water sumping policies, or different operator fuel system procedures.

Boeing suggests 777-300ER and 777-200LR operators review their operation for exposure to trapped center tank fuel and their maintenance policy related to water sumping.

We recommend operators establish a policy to monitor center tank fuel quantity upon arrival of each flight. If trapped center tank fuel above 400 lbs (200 kgs) is discovered, we recommend a further review of fuel reserve and maintenance policies as noted above.

If operators chose to address this issue by uploading additional fuel, Boeing recommends operators notify their flight crews that additional fuel has been loaded to mitigate the potential for up to 2200 lbs (1000 kgs)of unusable fuel following failure of the scavenge system.

For operators who have seen the trapped center tank fuel condition and chosen to adjust their fuel reserve policy, we recognize it may be possible for this condition to be resolved on future flights due to a change in environmental conditions or maintenance practices.. If this situation arises, we believe it appropriate to adjust fuel reserve policies to original levels provided they continue the monitoring policy on a flight by flight basis for trapped center tank fuel.

Although these failure to scavenge occurrences have only been reported on the 777-300ER, any Boeing recommendations should also be applied to the 777-200LR as it has an identical center tank fuel scavenge system.


If further information is needed regarding the subject, please contact your local Boeing Field Service Representative. If your local Field Service Representative is unavailable, you may contact the appropriate Airline Support Manager or call the BCA Operations Center at (206) 544-75

in summary - boeing are aware of an issue with teh fuel scavenger system where there could be fuel on board but the tank being used potentially could run dry.

reply to post by Harlequin

Nicely found Harlequin, could you please post up the link to the source material I would like to take a further look.

LEE.

reply to post by thebozeian


sadly i can`t suply the link as it was found on a certain `pilots rumour` forum.

[edit on 7/3/08 by Harlequin]

reply to post by thebozeian


Google "UPDATE: AAIB investigation into BA38 B777 crash at LHR". First result. Page 31. The 777 in question was a 772ER, NOT the 773LR or 772ER which had the scavenge pump issue... unless they're the same?

[edit on 7/3/2008 by C0bzz]

Originally posted by Zaphod58
From my understanding of fuel pumps, once cavitation starts, it can stop on its own, BUT, you have damaged the fuel pump at that point and it may not pump as efficiently as it was before the cavitation started. Cavitation is caused when SOMETHING creates bubbles in the fuel,

I don't know about fuel pumps... But I have seen the effects of cavitation in water pipes, it's an impressive process, it's said that as the bubbles collapse in on them selves (that's where the energy that does the damage is released) the friction and pressure results in a very high temp - and I'm talking about thousands perhaps tens of thousands of deg C for a tiny fraction of a millisecond.

In fact...

"When bubbles in a liquid get compressed, the insides get hot -- very hot," said Ken Suslick, the Marvin T. Schmidt Professor of Chemistry at Illinois and a researcher at the Beckman Institute for Advanced Science and Technology. "Nobody has been able to measure the temperature inside a single collapsing bubble before. The temperature we measured -- about 20,000 degrees Kelvin -- is four times hotter than the surface of our sun."

link

Doesn't sound real does it?? The method outlined for those results may not be totally relevant to fuel in a fuel pump - they were measuring cavitation in liquid blasted with sound waves above 18,000 cycles per second. But just goes to show what a erosive force those little bubbles can be.

The DFDR (black box) on the AA flight which had one engine delayed shows one of the throttles did not move when requested for 10 to 15 seconds. This differs from flight BA38 where the DFDR shows both throttles moved when requested.

The working theory at this point is the First Officer had his hand on the
speed brakes during this time (verified by DFDR) resting his palm on one throttle preventing the throttle movement asked for by the auto thrust portion of the auto pilot.

summary:
The solid info (not theory) is something prevented the throttle from moving preventing the engine from revving up.

The theory is it was an external physical restraint on the actual throttle.

PS - I said it before Cavitation is being used for Nuclear Fusion experiements, using Acetone CH3-CO-CH3 with the normal H3 replaced
by Deuterium and tritium, thats how powerful cavitation is. Oh and
Neutrons are generated by the experiments.

I spent alot of time trying to find examples of cavitation hysterisis ie
once started its even harder to stop, I saw some formula's alluding to this
but they were all dealing with a closed system, SO I guess Zap is right
and the pilot who said once cavitation starts makes it very difficult to stop
without closing the throttles, was FOS. Would have been a nice theory (maybe still is??)

There is some more info leaking out about the trip 7 - and none of it good for boeing:

www.flightglobal.com...

I would like to remind everybody that, according to a senior avionics manager at Honeywell in a paper published in a major conference, a certain aircraft type came within days of having its airworthiness certificate withdrawn in the early 2000's because of irresoluble problems with data transfer on critical data buses (known as "Byzantine faults").

and

From the URL above:

"Boeing's chief pilot flight operations safety division Capt Dave Carbaugh says the fact that the fuel pumps, according to the UK Air Accidents Investigation Branch (AAIB), had been cavitating not long before the impact"

Is my mind going? I only remember a statement in the latest AAIB report that there was damage caused by cavitation, not anything about when it might have occured. But does Capt Carbaugh might know something I don't?



what are boeing hiding.

Originally posted by stumason
reply to post by TheAvenger

 

Indeed!! An Indian work colleague of mine said had this been an airline such as India Air or Pakistan Airways, it would have plowed into the tarmac nose first. Apparently of all the airlines he's flown, with BA you hardly notice your landing.

even the passengers didn't even think they had crashed until the evacuation began, must have been that smooth a crash! I was once on a KLM flight from Heathrow to Schippol and it felt like the pilot really hated the tarmac when we got to Holland!

Well frankly speaking.. it is all about the air crew and not so much the airline in general.
I can vouch for that fact since I have flown in both BA and AI (Both in and out of Heathrow). AI has an older fleet as compared to BA, and that has a lot to do with it.

And as for your Indian friend, I don't know where he's coming from with his information, but I'd sure like to hear more on that front. Is he in the a/c industry?

P.S.: I'm flying out on a nonstop AI-777LR from NYC to Bombay in a month so hey... I'll let you know when I land!
lol.. Coincidences: Proof that god exists and he has a decent sense of humor!

So we currently pinning the root cause as the scavenge tank?

[edit on 18-3-2008 by Daedalus3]

It appears that boeing IS aware of fuel icing issues at low temps within the fueling system espeically the scavenge tank - the words from the chief test pilot saying the cavitation damage occured at the time of the engine throttle down really does say they know about it allready.


whay isn`t thew trip 7 fleet grounded?

One accident in almost 15 years with a fleet of almost 1000 aircraft. Take a guess.

[edit on 19/3/2008 by C0bzz]

Originally posted by C0bzz
One accident in almost 15 years with a fleet of almost 1000 aircraft. Take a guess.

[edit on 19/3/2008 by C0bzz]

theres alot more incidents than 1 accident - whilst only 1 aircraft has crashed - far far more than that have had serious issues.

reply to post by Harlequin


Yeah, and give me one example.

saudi arbia B777 5 days ago , wing spar failure on landing approach

The wing spar failed. Um, ok. And how exactly does a wing hold together if a wing spar snaps? How you came to that conclusion after watching a low resolution video on youtube beats me. How did you? The common consensus is a flap actuator failure, but I'm not going to claim anything. . As this has only happened on a single aircraft, it hardly warrants a grounding of one thousand aircraft. Neither does the scavenge pump. Until the report comes out, these arguements in favour of banning the 777 are trivial at best.

[edit on 20/3/2008 by C0bzz]

BA 777 engine control failure may have been caused by a electronic defensive jamming signal. Part of the Royal family took off just ahead of the BA 777 that was on approach. They think the signal interfered with the FADEC (Full Authority Digital Engine Control) of the engines. Its no wonder why there has not been anything in the news about the accident investigation. This is a bit embarrassing to say the least.

Birddog,
Do you have any link concerning the jamming signal interfering with FADEC? I am most familiar with GE specs for FADECS now supplied by BAE..I do know part of Qual involves EMI susceptability testing. I also have worked for a couple years on radar jammers.. Just wanted some more info if available.

BP

BP,
the information I received was verbal from a credible source. I have no link or further info.

BD