777-200ER Trent892 Fuel

[vc10derness]

Can a current pilot of the mentioned type give me, please, a guideline figure for fuel usage per engine at FL350/ISA+10/GW215.8? Doesn't have to be spot on. There's something that doesn't add up in an investigative simulation I'm running. Many thanks.

[mathy]

6500kg/hr, M0.83 total
so 3250kg/hr per engine

Next question.... there always is.

[vc10derness]

Thanks, Mathy. Yes there is but this might not be the place for it and I would need to formulate it very carefully. I need to investigate further.

[vc10derness]

OK, Mathy. Here is the next one (ish) without getting too deep.
Would you expect your ATC flightplan to list your endurance in fleet average fuel usage terms or your actual airframe? You'll gather that I've been out of a longhaul seat for some years.
Additional question. In your present company, would you be given performance-detriment specific ADDs before making a sector fuel uplift decision?
Last one for this time round: remembering forum etiquette ;), what would your response be when, after having made fuel uplift decision, you subsequently found out that on of your 892s was burning 1.5T per hour average more than the other....on a 5.5 hour sector?

[mathy]

No I am not biting

[vc10derness]

Understood. No problem. This wasn't relevant to my old longhaul outfit or, I suspect, yours....may be the same one.
Thanks for the input and I'll continue the simulations with what I've got.
(The incident was just over a year ago and is still unsolved.......)
There are things that are definitely not adding up when compared with the 585 page document so far produced.

[DevX]

1.5T difference sounds a wee bit excessive purely for T800 performance deterioration, unless there's a fuel leak of course.

This ESA PAD refers to one possible problem:
http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CA4QFjAB&url=http%3A%2F%2Fad.easa.europa.eu%2Fblob%2Feasa_pad_10_013. pdf%2FPAD_10-013_1&ei=PrkeVZPZFYnfaNTTgKgI&usg=AFQjCNFzYRRCvJOAPRZdQQuXb5pXGMA_zw&sig2=BoZF3REYpSTTRUHWMunyPg

[vc10derness]

Thanks, DevX.
Yes, I'm aware that the figures look huge (+/- 20%). That's basically why I'm trying to do this simulation. The figures are straight out of the ADDs in the Tech Log of a flight incident 1 year ago which has not yet been resolved. (Well reported internationally).
Something didn't look right and I'm trying to determine what it is.
Thanks for popping up. You current on type?

[DevX]

Not current on aircraft type, but current on all Trent engine types. :ok:

[yotty]

vc10, are you saying there was a performance ADD that stated an increase in fuel burn of 1.5t per hour with a specific DDG reference, or an ADD (not quoting a DDG ref) for an increase in fuel burn of 1.5t per hour? :confused: Within the company I work for, I'm sure the Drivers would be given OPDEF info stating any DGG related increase in fuel burn.

[BuzzBox]

That's interesting. The trip fuel stated in the factual information that was released regarding the said incident does not seem to take into account the extra fuel burn mentioned in the deferred defects. It's also interesting that the extra fuel burn had been deferred since Nov 2013, some four months before the incident.

yotty: The report only mentions a deferred defect where the right engine was reported as consuming 1.5T more fuel/hour compared to the left engine. There is no DDG reference mentioned in the report. It's hard to say from the information provided whether there was an ACTUAL difference in fuel consumption, or merely an indication problem. One would hope it was the latter given that extra fuel doesn't appear to have been loaded!

[DJ77]

I believe no sane maintenance department would dispatch and no sane flight crew would accept an A/C with such a discrepancy. To me the figure mentionned must be a typo.


Looking at the T/O and CLB reports, you can read the LH and RH fuel flows (WF) in lbs per hr. Converted to kg/hr the difference is 197 and 92 for T/O and CLB respectively.

[BuzzBox]

No, I don't think such a discrepancy would be allowed either, especially not for four months. The deferred defect states that the 'right engine consumes average 1.5T more fuel per/hour compared to left engine'. I'm wondering if they've taken that from the Left and Right Fuel Used figures on the FMS Progress page. Some kind of indication or FMS calculation problem perhaps?

[yotty]

Thanks BuzzBox you have more info than I. To verify what was actually happening, a comparison between the FMC figures and a simple subtraction of departure fuel against remaining fuel would hit the spot. Or am I missing something?

[BuzzBox]

Yes, a cross-check using the fuel quantities would show if there really was a discrepancy. The report doesn't say how the discrepancy was determined, so I'm only guessing it was an indication problem and it may have nothing to do with the FMS at all.

The FMS takes a snapshot of the fuel quantity at engine start and then uses fuel flow to calculate fuel remaining and fuel used. If the fuel flow information sent to the FMS was in error that might account for the discrepancy. Impossible to say without further information. Perhaps all will be revealed when the final report is issued, if ever.

[DJ77]

The source of the entry into the deferred items log appear to be some engineering staff. If it had been an indication problem I believe the complaint would have been raised by crew.

[BuzzBox]

Yes, perhaps it was a typo as you said. If it was a typo perhaps it was actually referring to OIL consumption rather than fuel: "Right engine consumes average 1.5QT more oil per/hour compared to left engine"??

[yotty]

BuzzBox, an oil consumption that high would have grounded the aircraft immediately! :=

[BuzzBox]

Quite right. I must remember to engage brain before opening mouth!:O

[DJ77]

Perhaps the original log entry was 1.5 %, not 1.5 T. That would be close to what is shown in the T/O and CLB reports.

[Mechta]

Maybe this a bit of a long shot, but having been told of the sizable lumps of ice which have been known to form in aircraft fuel tanks over a number of flights, if the conditions are right (dissolved water freezing out, and large amounts of condensation from frequent descents through moisture laden air) could the imbalance have been caused by one of these melting? This might give an increase in fluid flow, although the fluid would be fuel with a significant water content from melted ice.

AIR790C: Considerations on Ice Formation in Aircraft Fuel Systems - SAE International (http://standards.sae.org/air790c/)

I'm struggling to see how ice could form or melt in one side only; however the way the aircraft was parked relative to the sun might explain that.

This is not the BA038 scenario, more a case of a build up from condensation over a number of flights in the outer part of the tanks from a succession of flights and then parking in conditions sufficiently cold that the ice build up did not melt until the flight in question.

[yotty]

Could be Mechta, but BA have been hot on carrying out fuel tank sump drains, and are done routinely. If water is present in the fuel there will be also be a message on the fuel maintenance page. :)

[Mechta]

Yotty, The water detector is an inverted ultrasonic fuel probe which looks for the water/fuel interface, and is fitted at the inboard (lowest) end of the tank. If the water in the fuel didn't make it to the water detector, having frozen first, or was so much that the water detector was fully submerged (from what I remember, its only about 6 inches tall), then perhaps it wouldn't have shown up on the maintenance log?

[yotty]

I guess that is entirely possible Mechta!