FirstStep

Report states that crossfeed valves were closes for entire flight...and 10K fuel balanced for the most part in the two main tanks....
Was center tank fuel uploaded for this flight, and if so, roughly how much?.
As I am unfamiliar with the 777 ( only the 747-200 & -400 ), are the CWT fuel boost pumps "override" pumps, as in the type that will put out more pressure than the mains?. And if so, is there any limitations to having them on below a certain volume?. Could there be any possibility that CWT fuel ( mabye unscavenged fuel ) at highpressure was feeding/cavitating both engines?. Would only the pump cavitate, or would air be induced into the system?.

I know SOP would most likely have had Center tank emptied by now, and pumps switched off, but again I'm looking for a "common feed" so to speak.
Again, I am unfamiliar with the 777, and I know there is a wealth of knowledge spread ( unevenly ) amongst those who peruse this forum.
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As far as the kudos for the "wonderful" job the Autopilot did...
If I were handflying this approach, and lost thrust, would I sacrifice altitude for airspeed ( to prevent a stall ), damm fckng right I would.
And YES, with a loss of thrust, I KNOW I could FLY it to the ground a WHOLE lot better than the A/P. This is airmanship 101 guys. The only question I have is at what point do I realize I had no thrust and then act.

As I have no doubt there are those that will lay into me....lube liberally pre-applied.

Wornout Rubber

It seems apparant that the A/P remained engaged down to 175 feet. Although the A/P is a pilot`s best friend in most emergency situations, perhaps it was not the case in this instance.

The speed at 750 feet must have been about 140 Kts.
The speed at 200 feet was 108 Kts.

As the the A/P was engaged, the AFDS was trying to maintain the glideslope, with a probable linear speed decay. The speed loss was approximately 32 kts in 500 feet.

Every kt of speed below VRef 30 would result in a worse Lift/Drag ratio, with the result that the aeroplane could not eek out as much distance as it potentially could if it was flying at it`s best L/D ratio speed (approx VRef). At 108 Kts, the L/D ratio would be significantly reduced.

VNAV PATH

Hello,

New member in this Forum , and flying 777 outside UK .

My SOP seems quite different than the one described : mine is telling that ( except Cat 2/3 ops ) PF is flying whole sector : no hand over in approach .

Does BA SOP mean the PF has the controls until TOD and take it again at 1000 AGL ? And what reason motivate such a practice ?

Am I correct ?

Thanks !

avrflr

About 20800kgs, depending on S.G.

CONF iture

Thanks for that clear explanation, I was as surprised as MU3001A, but discovering that specific BA procedure (?), AAIB report makes now more sense.

What still does not make any sense considering that almost simultaneous double eng similar misbehaving:

1- "total fuel on board was indicating 10500 kg" ... but no mention of the actual FOB retrieved from the main tanks ?

2- "the fuel crossfeed valves indicated that they were closed" ...but no mention they have been physically checked closed ?

Also:
- What could justify that amazing 5% reduction over the planned fuel burn ?
- Did the engines actually spool up somewhere in the hold ?

phil gollin

Quote :

Phil,
The speed is controlled by the fuel going to the burners, N1 in my book, this is determined by the demands of the throttles set by the crew. This is basic gas turbine operation.

unquote

I meant the speed of operation of the fuel pump.

The fuel valves were open, the throttles (and auto-pilot) demanded an engine speed higher than that acheived, the actual speed of the fuel pumps doesn't seem to have been stated in the special report.

.

HotDog

Milt,Not so, the fuel from the aircraft supply system (read tank fuel booster pumps) is fed into a compined LP and HP fuel pump assembly on each engine.

Mr @ Spotty M

How can the total fuel on board be measured when an amount is soaking into the grass at the crash site.
Could this be why they AAIB state indicating?

TheInquisitor

Somebody mentioned electrical disruption further back in the thread, and I feel it may merit some thought here.

Question - are the tank booster pumps normally in operation in this configuration all fed from the same bus? (not a 777 operator, BTW - I'm assuming here that they're the standard 3-phase type commonly employed).

Reason being, I have come across an odd mode of electrical failure on a previous type, whereby a single phase on a single bus tripping off creates all sorts of oddities - the cause of which are not immediately obvious, since a motor with a dead phase acts as a generator on that phase (still being driven by the 2 good phases) preventing any indications of electrical failure, but sending oddly-shaped wigglyamps to other components.

Might be a worthless tangent, then again, might not be. Just something else to throw into the collective headscratching!

Volume

Some new AAIB statement could be found in the Guardian today:

And the Telegraph writes

NSEU

On reflection, I think we can safely ignore the bits and pieces in the tanks as causes of fuel starvation (scraper, paper, etc). Remember that there are 2 pumps in EACH tank. All four tank pump inlets would have to be blocked to cause the problems seen. Each pump is designed to provide enough pressure/flow to supply the onside engine with fuel for all flight regimes (and probably more). The lowest spec I've seen for a 777 wing tank pump is 12psi and 16tonnes/hr

I don't have the wiring schematics handy, but I believe the L/R wing tank pumps are powered by their onside Transfer Busses.

Rgds.
NSEU

PBL

TwinAisle cites Private Eye's article, and says "clearly there are elements that don't add up".

There are two major points that "don't add up".

First, the article asserts that FBW systems before the B777 were triple-redundant, designed/written/implemented by three separate teams. That is rubbish.

Second, the article concentrates on the PFC (and maybe on the AIMS). I don't think anybody has suggested there was something wrong with primary flight control.

PBL

sky9

Just a thought for the boffins

AAIB report:
If there was a restriction upstream from the HPFP’s would the effect be to cause the pumps to effectively stall and prevent them from working? A cavitating pump does not generally pump much even if it is: Such a scenario would account for only minimal amount of fuel reaching the engine. Has there been a fleet check of the pumps to ascertain whether this is a one off or a common defect?

There is also a major discrepancy with the planned fuel burn and the actual. Planned burn including taxi fuel would work out at 72,000 kgs actual burn to short finals was only 68,500 based on the AAIB figures. Was this based on FMC fuel indications or gauge indications?
Unless there was a reason for a 5% difference such as an improved route or altitudes it seems a little large to me.

bubbers44

Seems like any pilot dealing with decaying power as this was would put speed control requiring to push the nose down below the requirement to not hit the ground before an obstacle. Clearing the fence and hitting a flat surface saved the people in this case so the pilots did all they could under the circumstances even though they had to sacrifice speed to do so. All they could have done was possibly add flaps before hitting the ground to get closer to the runway.

NSEU

The CWT pumps put out more pressure/flow than the wing pumps. Low pressure output at the CWT either due to the pumps being switched off or due to no fuel in the tank will cause the check valves on the CWT pumps to close, preventing air getting into the manifolds. Like the 744, this process will occur well in advance of landing. Remaining fuel is scavenged via jet pumps (and as discussed previously, this process completes well before a normal landing).

I believe someone asked earlier.... There is no gravity feed for the CWT.


...but if pulling back on the stick with the stickshaker ringing in your ears for a few seconds longer meant narrowly missing a large building (and you knew there was a flat surface beyond)? Wouldn't you take the chance that all those built-in margins for stall might work in your favour on that particular day?
Personally, I think man is a gambler... He is taught what is impossible, but when faced with a large immovable object, he goes for the impossible

swiss_swiss

phil - you asked about the speed of the HP fuel pumps and how they are controlled - it should be noted that the pumps are not electrical driven but are connected to the the gearbox and as such the gearbox is driven via a shaft which is in turn connected to the N2/N3 compressor spool so the pump speed is not and can not be directly controlled.

regarding the theories about a missing phase from the IDG, this would be sensed and the idg would be disconnected immediatly so that is a non starter

TheInquisitor

swiss_swiss,

All things being equal, I agree. But I have personally seen a failure mode where a dead phase on a bus was supplied with enough voltage to keep the genny / bus from tripping off, via the two still live phases powering an electrically driven hyd pump. A generator and a motor are essentially the same thing - you spin a motor with a dead phase, and it will generate on that phase and feed any component connected to that phase on the bus. Frequency lockout wouldn't necessarily pick it up either, if the remaining 2 live phases of the motor could draw enough juice from the bus to keep it spinning at close to its normal running speed.

Make sense, or am I not explaining this very clearly? Just to clarify, this isn't idle speculation, this has actually happened to me (on another type, considerably older than 777)

Sven Sixtoo

Phil

If it's anything like the Fuel Control Unit on my aircraft (which also has R-R engines), the HP Pump pushes out considerably more fuel than the engine needs. A variety of spill valves bleed off fuel for various reasons. The most important is a system that ensures a constant pressure drop across the throttle valve. Adjusting that valve then produces a given flow for a given setting regardless of what the pump is up to (within limits obviously). The electronic side of the engine control adjusts the throttle valve, and a monitoring system tells the electronics whether or not the desired result has been achieved.

What seems to have happened here is that the desired result was not achieved, so the electronics continued opening the throttle (that's all they can do in the last analysis) in order to get the desired result - which didn't happen.

swiss_swiss

hi inquisitor

your description i can easily follow and can understand how that could be possible. ( i am well versed in motor/generator theory).
mind me asking which type this defect was on and how the system was monitored?

AFAIK (would have to go back and look at my training notes) each individual phase of the 777 is monitored so if 1 is missing then the gen is switched off - would have to confirm this tho.

phil gollin

Re. Fuel pumps.

Thank-you "Swiss Swiss" and "Sven Sixtoo".

If I have got it right, the fuel pumps work continuously at maximum rate (when switched on) and the actual fuel flow to the engines is controlled by the control valve AND spill valves which get rid of any excess pressure.

Are the spill valves actuated, or merely like saftey valves, operated mechanically by excess pressure ?


Thanks

.