111boy

come on...a fat test is obvious, who would trust a skinny pilot ?

airfoilmod

One of my suggested possibilities 300 posts (or so) ago. I also suggested the possibility of ethanol contamination as well, (explaining an unusually low fuel freeze point also: -57). This would increase "fuel" susceptibility to disastrous vaporisation at the HP pumps and consequent cavitation/damage to pump lobes. Although the AAIB tested samples, and they tested "OK", it isn't possible to have tested "all" fuel. Forgive the poor Physics memory, Wily. Something else that could have found its way into the tanks by mistake is Glycol, or DeIce fluid.

skiesfull

"Dear Willie,
Sorry I f****d-up the landing - it's because I'm a fat b@st@rd."

Smilin_Ed

There has been much discussion as to whether faulty software or Electromagnetic Interference (EMI) played a part in this accident. Before we can ascribe fault to either, we need to know just what the software does. The fuel control has multiple inputs but, presumably, only two outputs, fuel metering valve and inlet guide vane positioning, both of which have been reported by the AAIB to have functioned properly.

What else does the fuel control ultimately do? If the fuel control does more, can someone help us out here? If not, to blame the software or EMI looks to me like barking up the wrong tree. Again, apparently appropriate electrical signals reached the engines and individual parts of the engines responded accordingly but the engines just didn't produce the demanded power.

If there are no other fuel control outputs, it would seem that, since the high-pressure fuel pumps have been reported by the AAIB to work normally and there was enough fuel flow to keep the engines running at just above flight idle, it boils down to some characteristic of the fuel which reduced its ability to burn properly OR some flow restriction, presumably upstream of the high-pressure pumps.

Of course, there is a third possibility, the tanks simply started to run dry.

wilyflier

Skies fool,
At least I`ve done more good ones than bad ones
Hillyflier

skiesfull

Me too, Hilly -I just couldn't resist it. Dreambuster's "blame it on the pilots for fat-induced decision-making flaws" belongs to the 'Aliens' post!

Hydroman400

Yes....indeed, I think someone has been on the blow . " While at 600ft, all I could think of was a fat juicy big mac....yyyyyummmmmmmmm, then all of a sudden we hit the ground....but it's not my fault, the burgers altered my mind...."

Squawk_ident

On the 29/02 on the french "rcoco.com" forum, one of the contributor joined to his post a report about the fuel scavenge system on the 777-300ER/777-200LR aircraft. I don't think that this (undated) report has been published here.
I believe it might be of some interest for most of you. And thank you for this very interesting discussion.
quote:

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

unquote

original link:
http://www.rcoco.com/viewtopic.php?t...=asc&start=600

Regards.

tanimbar

Squawk_ident's post is interesting, especially where it says:
"Indications are that the water in the scavenge system is freezing prior to discharging in the main tank. Frozen water (or ice) in the scavenge system could result in a low rate of scavenge or no fuel scavenge. "

But the report does not comment on what effect such frozen water would have on systems 'down stream' of the scavenge system.

Seems to be an odd omission but I assume Boeing concluded that it was not worth comment.

regards

Smilin_Ed

If there were fuel trapped in the center tank and if the fuel quantity system were working properly, the crew should have noticed it. AFAIK there has been no report that the crew noted anything less than sufficient fuel in the feed tanks to make a safe landing. If the feed tanks did run dry, that points to a fuel quantity indication problem.

grebllaw123d

I qoute from post #608:

"On the 29/02 on the french "rcoco.com" forum, one of the contributor joined to his post a report about the fuel scavenge system on the 777-300ER/777-200LR aircraft. I don't think that this (undated) report has been published here."

According the AAIB reports, BA38 was a 777-236ER.

It appears that this SB is valid only for the -200LR and not for the -200ER

SpeedyG

May seem irrelevant, but can we rule out the fact that the temperature was so cold the fuel was gelling and perhaps that led to the scavanging effect.

After impact etc this would possibly not be detected??

seekayess

The Manager, OzJet, Safety & Security has posted the following:

My knowledge not being up to scratch on the subject, thought I would run it past you folks!

Green-dot

Quoting Smilin Ed:

According to the AAIB report, engine fuel control systems functioned normally. However, if fuel flow (from airplane fuel system) to the engines is somehow restricted and cannot meet engine (control) demand, the engines will only accelerate to- and stabilize at the restricted fuel flow value, regardless of normally functioning fuel controls on the engines.


Green-dot

Chris Scott

Quote from ArcticLow [Mar02/19:06]:
....At 1000ft radio, the F/O takes control, states "Man Land 280 baro", but leaves the automatics in. At this stage, everything looks OK and they're just waiting to lose the last few knots of extra speed and so the power still hasn't come up fully. They've already discussed this and agreed that idle power is OK at 1000 but they'll go around if still not fully stabilised by 500 radio, as per SOP. At just under 750ft, the speed reaches the bug, the levers move forward to maintain target speed, but nothing happens. The levers go to climb power, still nothing. The F/O applies TOGA power, nothing. The rest is in the AAIB report. I don't know if this is what happened, but it's starting to look like a high probability hypothesis, on the available evidence. Thank God it wasn't a scarebus...
[Unquote]

For someone who claims not to be a pilot, you are remarkably well briefed. Perhaps by one of the Boeing Airways pilots on a long overnight flight?
He has certainly sold you the whole package -
1) If a Boeing has an incident/accident, it cannot possibly be caused by any fundamental problem with the aircraft. Possibly rogue fuel?
2) If an Airbus has an incident/accident, it's because the designer was simply bonkers.

Sound familiar? So, since you have begged the question, can I stay off-topic to speculate what MIGHT have happened if the Trent engines on an A330, for example, had behaved like the ones on G-YMMM did, at the same point on the same approach?

Unlike the B777, the A330 autopilot would be programmed to Go-Around mode as the pilot selected TOGA thrust. Because the aeroplane would be unable to comply, the AP would drop out almost immediately, and the FD demands on the PFD (ADI) would be of no help. The PF would switch it off (or ask the PNF to do it).

"Fly the aeroplane." The FBW would be doing just that. It would maintain 1-G flight in pitch, and zero-rate in roll; holding a steady descent path and keeping the wings level (if they were when the AP disengaged). Because of the shortage of thrust, the speed would be decaying, as per the B777.

Workload permitting, the PF might select the FPV display on his/her PFD. This, with the FD switched off, would display the "Bird", a symbol showing the drift and descent trajectory. This might be useful to check a steady profile is being maintained initially, even though the nose is being raised steadily as the speed falls. Because of this, the "picture" of the world outside the cockpit windows is starting to look very wrong.

Meanwhile, the aeroplane is still pretty much on the glide-slope. The FBW continues to run the stabiliser-trim in the "nose-up" sense. A decision must be made. The PNF's attempts to revive the engines have failed; we are going to undershoot the runway. What is the best (minimum-drag) speed on this aeroplane with landing flaps and gear extended? Haven't the foggiest idea, but we must be already below it! Time to trade height to stop the IAS going any lower. Slowing down equals MORE DRAG. We'll have to maintain this speed as long as we can. Tweek the sidestick forward a bit, then release. Down we go, is that enough?

We've got to get over the perimeter road – which has already disappeared somewhere under the nose – and into the field. The speed is still decaying slowly, unfortunately, but this aeroplane cannot be stalled. As the IAS drops to Alpha-prot, about 13% above stalling speed, the stabiliser stops trimming back; the stick must now be pulled harder and harder to stop the nose dropping. Can we keep a tiny bit of speed in hand to avoid hitting the ground too hard?

The rad-alt calls "ONE HUNDRED". Pull a bit harder. "FIFTY". Stick hard back - we've got to miss that road. We're close to Alpha-max (5% above stalling speed). Now, the aeroplane will descend of its own accord to avoid stalling. "TWENTY", BANG, we are down...

DC2 slf

Smilin Ed said:

"There has been much discussion as to whether faulty software or Electromagnetic Interference (EMI) played a part in this accident."

EMI, like "pilot error" is something which leaves little or no evidence behind, and so is a convenient explanation for otherwise inexplicable events.

Modern airliners emit a lot of radio frequency radiation for many purposes, and their instruments and controls are made to tolerate quite high levels of EMI.

infrequentflyer789

Also the AAIB should have noticed, and their report says:

The total fuel on board was indicating 10,500kg, which was distributed almost equally between the left and right main fuel tanks

Milt

Engine Compressor Guide Vanes?

Could I recommend we should look at the part that the engine guide vanes play in the scheme of things. They have received precious little attention so far no doubt because of the concentration in trying to determine a single source for a two engine event.

Presumably the engines compressor guide vanes angular control is by the FADECs which are in turn are driven by dedicated computerised software. Wonder where the FADEC software is physically located.

Can someone describe the Trent guide vane system? How many stages of vanes and are they all interconnected? Over what RPM range do they do their thing? Are they hydraulic, fuel pressure or bleed air driven? Are they anti-iced and what is likely to be the effects of malfunctioning or non functioning during engine acceleration?

Chris Scott

Quote from grebllaw123d:
According the AAIB reports, BA38 was a 777-236ER.
[Unquote]

Hi, Are you are under the impression that the Boeing Service Bulletin only applies specifically to B777-300ER and B777-200LR?

Think you will find that Boeing dash-numbers ending in "0" or "00" are a kind of generic description. The second and third numerical digits merely indicate the airline.

Since I was a lad, all Boeing airplanes bought new by BOAC and BA have had dash-numbers ending in "36", e.g., B707-436, et cetera.

Chris

Editing PS: Ah, now I see what you mean, I think. Is it the "ER" designation you are querying? If so, I don't know. Sorry.

Oldlae

Chris, read post #608 the SB refers to 777-300ER and 777-200LR not 777-200ER.