fuel temp
 

You can overwrite the fuel freeze point on the FMC.

You noticed that too, did you.....

Sorry, I thought you (or someone else) was saying that leaky seals were the root cause of the cavitation problem.... rather than a blockage downstream. Yes, I suppose air might get in through leaky seals with a vacuum in the lines.. but neither air nor vacuum are very good for running engines :)

Pumping hydrocarbons (aka fuel)
 

HP pumps, be they gear (positive displacement / lobe) or centrifical, behave very strangley under many conditions that are just marginally outside of the nominal state. Any one variable can have significant impact to pumping performance. (Cavitation pitting is the clue!!!)
Variables include:
Turbulant vs laminar flow at LP side (Reynolds Number).
S.G. variation at temp deltas (pumps are pre set for nominals NOT all temps).
Clearances and gaps between rotator and stator faces are critical, too big equals deminished performance, too tight equals tip gassing (cavitation).
Contamination (even at < 25 micron level) plays havoc with the flow transition state across the face of the impeller. (Again cavitation).
Cavitation pitting is NOT an instant catastrophic occurance it is a chronic progressive development.
I am sure that many engine HP pumps exhibit similar pitting but I believe that we have a concoction of variables that culminate in an event of the HP pumps creating an air (gas) saturated "fluid" on the HP side that is inadequate to provide the combustion energy required for thrust.
Please, if the AAIB lurk here, look outside of aviation for similar examples of HP hydocarbon pumps behaving very strangly outside of the norm.

Cavitation

You don't have to have air at the HP pumps' inlet to result in cavitation. Cavitation will occur when the pressure is lowerd sufficiently to reach the 'boiling' (vapourisation) temperature of the fuel. That pressure may be
close to a vacuum for fuel already at a very low temperature.

It could well require the services of a Methusela to know just when cavitation damage occurred in the pumps. This could have happened during any periods when there were no booster pumps operating at high altitude with warmish fuel. Cavitation damage occurrs when the pumps lose their continuing lubrication by the fuel itself.

Can any boffins out there give us an idea as to the specific vapourisation pressures of jet fuel over the warm to cold temperature range?

This may be a bit of a useful learn for those who don't already know the dangers of cavitation with jet engine HP pumps.

Just a thought.

http://i38.photobucket.com/albums/e1...tonboy/27l.jpg

Troy W … was it only diversion from your friend or was it real leaks or other controlled rumors by THE WSJ ???

… I still expect AAIB would have mentioned any of that … !?


But to be honest I was waiting for a little bit more after 30 days:

-- From FL110 to FL90 in 5 min … surprising they didn’t need any slight thrust increase for that period … How did the engines react ?

-- I know they maintained maybe for a few hours 3000 ft above the planned FL and therefore were probably closer to the optimum, but still they had to hold an extra 5 min, so how to explain they managed to save an impressive 5% on the planned fuel burn ?
Was BA flight planning so much way out, or is there anything else … ?

-- What does mean “The FO took control for the landing at a height of approximately 780 ft”
did he just come back from a pee … or the CPT fell incapacitate … ?

Anyway … “The recorded data indicates that there were no anomalies in the major aircraft systems” … and fuel was not an issue … but still, 100% of the engines refused almost simultaneously to produce the requested thrust ........................................?

Best Glide Speed
 

Can anybody comment as to the best lift/drag speed (best glide speed), with Flaps 30 on a B.777?

The AAIB stated that the speed decayed to 108 Kts.

I don't recall seeing anything in the report about filter bypass warnings? Is it possible the problem is somehow after the filters but before the pumps that cavitated?

Likewise no mention of the flaps being raised.

Discuss...
 

As my posts appear to dissapear like ice and wax in a fuel line, can anyone who knows what they are talking about explain this quote?

Sure what it says is that at a height (distance above the ground) of 720 feet (1 foot = 12 inches) the right engine ( motor that converts thermal energy to mechanical work) thrust (reaction force) reduced (got less). Some 7 seconds (unit of time) later the thrust on the left(opposite of right) engine reduced (got less) to a similar amount. The engines did not shut down (stop) and both engines(left and right) continued to produce thrust at an engine speed above (more than) flight idle(minimum speed in flight) but less than the commanded thrust. (amount of thrust wanted by people at pointy end)
:hmm:

soggy_cabbage: That quote seems pretty self-explanatory. Which part don't you understand?

Edit: Nice one daysleeper:D

Quote:-


unquote

It is interesting to think what could actually cause two separate engines, fuel pumps, filters, etc.... to reduce thrust to "a similar level" but not at the same time.

It is the "similar" which is so intriguing. They could have used so many words and that one could mean anything or NOTHING.

.

At a previous airline I worked for, they had a almost brand new widebody aircraft, suffered a serious engine surge/stall just after rotation. Shortly after engine recovered to required thrust setting, but with abnormal indications (EGT etc). Fuel dumped and aircraft returned. Engine was changed due to internal damage. New engine suffered same problem 2 days later. Extensive investigation revealed plastic pipe blank lodged in fuel feed pipe in pylon area. During high thrust setting, ie take off, fuel flow to engine HP pump was blocked, then almost immediately cleared, then blocked again, causing fuel starvation etc and surging. Initial problem was put down to failure of the original engine, as after the replacement was fitted full power runs were carried out. Offending plastic blank was traced back to manufacturer....

No, but it's not the minus 70 that the single aisle airbus's are limited to. After flying the airbus it was something I looked for and it isn't in any of the manuals (BA) so the 777 can be flown in colder air.

Some posters here have mentioned at what temp the low fuel temp warning would activate. On BA 777's the fuel freeze temp can be changed in the FMC but is set to -40 by default, the actual warning starts at 3 degrees above that value. So by default (but it can be changed) he low fuel temp warningwould sound at minus 37.

Who manufactured the fuel pumps - is it Goodrich who supplies it along with the FADEC?

Debris
 

Just as an aside, the debris found in various locations in the fuel system:

- a red plastic sealant scraper
- a piece of black plastic tape
- a piece of brown paper
- a piece of yellow plastic.
- a small piece of fabric or paper
- a small circular disc

Surely this can't be normal. Was it all likely introduced during manufacture, or at later stages during maintenance or refueling?

I don't think you'd describe the debris as particularly abnormal. Fuel tanks often have bits of FOD floating around in them. Try to visualise a 6mm diameter plastic disk and think if you are going to be able to spot that in a large, dark fuel tank.

What this seems to be pointing towards is the only situation in which both engines could possibly have suffered the same fate - an as-yet undiscovered maintenance error either at Cardiff, London or Beijing; or more unlikely, a manufacturing defect.

As so much has been ruled out so far, it is even more likely that it is a seemingly minor circumstance that could have caused such an event. What that event is, however, clearly remains a mystery...

Goodrich supply the FMU, EEC and Actuator suite, not the Pump on the T800.