AAIB BA38 B777 Initial Report Update 23 January 2008

[avrflr]

Originally Posted by Stoic

In an ETOPS aircraft, would it not be more sensible to have completely separate temperature monitoring systems for each fuel tank/engine system (disregarding the centre tank)?

Or indeed any large aircraft. If there are big lumps of frozen fuel in your tanks, having four engines wouldn't be much consolation. It is surprising that there appears to be a single point of failure which could cause the loss of an aircraft. If the temperature probe fails completely, I imagine it would trigger an EICAS message, but what if it gives an erroneous but reasonable indication? If you are flying a long sector in unusually low OATs and you don't get a FUEL TEMP LO message, would you descend as a precaution?

OTOH, if the fuel freezes, surely the filters clog, you then get an EICAS message or two and then it's not such a surprise when the engines stop working properly.

[Stoic]

avflr

Thank you for your thoughtful reply. My concern is that there should be a common source of information for what, in my opinion, should be totally separated systems in an ETOPS aeroplane.

For completeness, I should add that I declined to bid for the 777 because I was unhappy about flying commercial PAX over exposed routes on 2 engines.
But I am a wimp and proud of it with a record of 13 engine shutdowns on a 747!

Regards

Stoic

[barit1]

Stoic admits:

But I am a wimp and proud of it with a record of 13 engine shutdowns on a 747!

Statistically speaking, you must have over a million hours in the logbook!

[exeng]

Barit1

Actually in the early 747 classic ops (and before my time as an F/E or pilot) a 4 engine landing was practised in the sim as it was unlikely you would ever experience the event on the line - or so the joke went! The shut down rate was appalling in early 747 ops, so 13 shut downs whilst unlucky probably is not a record.

As a ground engineer on the early P & W JT9D-3 powered 100's we used to meet each arrival with cases of oil to top up the engines. Turbine boroscopes used to reveal remarkable results and you wondered how the engines continued to function.

I'm certain that the original classic would not be certified today simply because of the awful reliability of the donks.


Regards
Exeng

[ChristiaanJ]

Exeng,
One cannot help but wonder if the guys in the 4-engine flame-out due to volcanic ash somewhere over Indonesia, so many years ago, had already practised it in the sim, too......

[Krimi]

Since there is so much speculation in this thread I wonder nobody brings up the fuel scavange system.

Is there one on the 777?

[exeng]

ChristiaanJ

One cannot help but wonder if the guys in the 4-engine flame-out due to volcanic ash somewhere over Indonesia, so many years ago, had already practised it in the sim, too......

They hadn't practised it I'm sure - none of us had. All of the current QRH checklists for total engine failure on Boeings, and I think Buses, are based on what F/E Barry T. Freeman actually carried out on that event. Must be nice to be remembered as the the bloke who invented a checklist on the spur of the moment that all operators worldwide now use.

Apologies for thread creep everybody.

Back to the wax. -47; -50 etc etc.


Regards
Exeng

[exeng]

Krimi

Is there one on the 777?

A fuel scavenge system that is.

Yes there is, and although I know absolutely nothing about how the AAIB investigation is developing, I would imagine it is not centred on the centre tank scavenge system. I could be wrong.


Regards
Exeng

[ChristiaanJ]

Exeng,
Thanks for your little spot of thread creep, and I mean that sincerely.

Even more so since the "ice in your juice" subject now seems to have been covered, fully and completely. Maybe the AAIB would like to comment again.

[exeng]

ChristiaanJ

I confess to being more than a little confused by your thanks. PM me if you want.


I had discussed the possibility of fuel 'waxing' with a BA mate of mine a day after the event and we both agreed that such an event could cause the 'irregularities' that were seen on that day - we discounted 'fuel icing' for the obvious reasons.

All of us airline types were bound to start speculating as to causes and so BT made a fortune as we chinwagged the issue. I came up with the idea of waxing as a cause that would affect both engines - but I then shot myself down because I felt that the effects of 'waxing' would have been realised much earlier.

Meanwhile I await patiently for the AAIB report.


Regards
Exeng

[Green-dot]

Scavenge system

Quote:
"Since there is so much speculation in this thread I wonder nobody brings up the fuel scavange system.

Is there one on the 777?"

Yes, there is:
There are four water scavenge jet pumps and two center tank fuel scavenge jet pumps.

Main tanks:
Each main tank has one water scavenge jet pump.

Center tank:
Each side of the center tank has a water scavenge jet pump and a fuel scavenge jet pump.

Fuel scavenge:
The fuel scavenge jet pumps take fuel from the low points in the center tank and send it to the main tanks. Float-operated shutoff valves prevent fuel scavenge when the main tanks are full. Inlet float-operated shutoff valves prevent motive flow to the jet pump until the center tank is almost empty. This prevents the fuel from flowing to the main tank too early if the outlet float-operated shutoff valve fails. A check valve in the jet pump prevents fuel movement from the main tank to the center tank.

Water scavenge:
The water scavenge jet pumps take fluid from the low points in the tanks and send it to the fuel pump inlets. This prevents water from collecting in the bottom of the tanks.

Operation:
The scavenge pumps (both fuel and water) operate automatically when the fuel pumps are on. They use fuel from the fuel pumps as motive fuel. The flow of the motive fuel through the jet pump causes suction that takes fluid from the low point in the tanks.

[exeng]

Well done Geendot

That puts my "yes there is" into perspective doesn't it!


Regards
Exeng

[NSEU]

Is it sensible to have the same single fuel temperature sensing system for both fuel/engine systems on an ETOPS aircraft?

In hindsight, you would have to say no. By the way, British Airways 747-400's have 2 probes (in the same tank), with a switch in the cockpit to select either A or B probe (for MEL relief), but as far as I know, there is no automatic monitoring to compare the two probe temperatures. You would only know if one had failed if the reading was blank or showing unreasonable values. Our airline and many others don't have dual probes on our 747-400's. I'll have to check, but I'm not sure if BA has a dual system on their 777's. I'd be surprised if they didn't (it would seem to be a backward step).

Anyway, I'll try to confirm this later today.

[FE Hoppy]

swiss_swiss FE Hoppy - mind telling me what you do for a living? I hope its not as a licenced aircraft engineer or pilot?

I refrained from commenting on the fuel/oil heat exchanger theory earlier in this thread but the question about the fuel filter is basic stuff.

of course there is a bypass mechanism for the fuel filter and a differential pressure system that indicates a clogged filter.

RANT ON

Swiss-Swiss, mind telling me where you learnt to be so rude? I hope it wasn't in a training centre in Zürich!!

I am not familiar with the engine in question so do not assume to know the layout of it's fuel system. I am familiar with some other engines and not all fuel filters are fitted with bypass valves and warning systems.

That is why I asked the question.

Now you claim to be familiar with this engine and I'm not going to question your credentials in public. So would you mind answering the question about the bypass system being overwhelmed?

And while your there would you mind explaining what use a filter bypass system is if the fuel flow has been restricted in the heat exchanger and pipes running to the filter? no pressure = no bypass as far as my understanding goes. But perhaps rather than making a positive contributions you would prefer to just insult people?


RANT OFF.

[Milt]

I've been learning something every day for more than half a century and now, thanks to this thread, I have a good grasp of the fuel systems of current heavies. But a couple of loose ends.

Are the B-777's high pressure fuel pumps gear type or swash plate piston ?
If gear type how is their output varied to control engine thrust/n?

Cannot conceive that there could only be one HP pump per engine.

[Stoic]

NSEU/Exeng/barit1

NSEU thank you for giving some hard information on the 747-400 fuel temperature sensing arrangements. I am looking forward to learning exactly what they are on the 777.

Exeng thank you for defending me while I slept.

The shut down rate was appalling in early 747 ops, so 13 shut downs whilst unlucky probably is not a record.

I see that my English was open to mis-interpretation. I was not claiming a record in the sense that I had the most shutdowns but was using the word record in the sense that it was my history that taught me to be a wimp. I would guess it is certainly not a record in the "most" sense.

Barit1. That might be the statistic in modern 747s but during the seventies the reliability was awful of both the P&W and the RR524. The fan on the latter was apt to leap from the front of the engine so had to be stopped at the merest hint of vibration. When BA first acquired the P&W-powered 747s and the pesky pilots were refusing to fly them (a squabble over money as I remember) BOAC were renting out their engines to other airlines that were flying and BOAC's aeroplanes languished at base with concrete blocks hanging from their wings. Incidentally I have a little over 17,000 hours, not all on the 747 but a mighty chunk!

Regards

Stoic

[gas path]

Milt

Are the B-777's high pressure fuel pumps gear type or swash plate piston ?
If gear type how is their output varied to control engine thrust/n?

The PAG (pump and govenor assy) has two pumps. The LP pump is a centrifugal type and the HP pump is a gear type.

As has (probably )been covered before. Fuel is fed from the tanks by the boost pumps rated at 12 psi for the wing tank pumps and 36 psi for the CWT pumps from there it passes to the LP side of the engine pumps, then via the FCOC which incorporates a bypass and a diff pressure s/w (for the EICAS indication) it passes to the HP (gear) pump where the pressure is raised for supply to the burners. From the HP pump it passes through the FMU (a lovely engineered piece of kit that is only the size of a small shoebox!)
The FMU contains the pressure drop and spill valve assy, the FMV and the HPSOV. From here the HP fuel is fed to the F/F transmitter and through to the burner rail via a small HP filter. (the HP filter being there to catch debris from a failed HP pump).
The pumps are driven directly from the HP gearbox and as such their output depends on ultimately (n3) shaft speed. Therfore unused fuel that is not required for combustion is returned to the inlet side of the HP pump via the P&D valve.
As a guess and from RB211 experience the output press. is in the region of 1200 psi at takeoff and less than 300 psi at crz.

[funfly]

Is there not a real problem that the press may be reporting based on postings here and pprune posters may then react to these 'reports' - chinese whispers?
It's a pity that this discussion area is being sourced by the media as it does place a responsibility on posters that maybe a discussion forum should be free from.
BTW, this has been one of the most interesting and informative threads for a long while especially for a GA driver like me.

[M.Mouse]

1- Would you tell me if the earlier mentioned BOEING COLD FUEL MANAGEMENT PROCEDURE was carried out in PEK

Quote:
if the fuel freezing point is projected to be critical for the next flight segment, Boeing advises the transfer of wing tank fuel to the center wing tank before refueling. This makes it possible to use the freezing point of the fuel being uplifted for that flight segment

I do not konw.

However, is that procedure not intended for use when the aircraft has been using fuel such as JET A with a FP of -40° (the normal uplifted fuel in the USA) not when the fuel used on the previous sector has been JET A1 with a FP of 47°C. Ex LHR it is highly unlikely that G-YMMM had had any fuel in its tanks which wasn't JET A1.

The fuel temperature after landing and sitting on the ground for half an hour or so would be (relatively) close to ambient air temperature. With a fuel load remaining of (typically for PEK) 7 tonnes and a typical requirement to uplift a further 63 tonnes for the return I would suggest that the uplifted departure fuel temperature would not be significantly lowered by the temperature of the inbound sector fuel remaining.

2- Would you know if BA038 had to hold anytime before landing ?

The aircraft did hold at LAM but for how long I do not know.

Is there not a real problem that the press may be reporting based on postings here and pprune posters may then react to these 'reports' - chinese whispers?
It's a pity that this discussion area is being sourced by the media as it does place a responsibility on posters that maybe a discussion forum should be free from.
BTW, this has been one of the most interesting and informative threads for a long while especially for a GA driver like me.

Ultimately this thread is of limited usefulness anyway! The exception being some excellent descriptions of the fuel system and other technical facts from people who plainly understand the subject.

I am sure most posts and what is written in the newspaper are taken with a pinch of salt by anybody with a degree of common sense (the least common of all senses).

[Flightman]

BAW38 did one circuit in LAM.