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flipster
20th Jun 2006, 17:36
Guys and Gals,

Does anyone know the reasoning behind recent Boeing and Airbus center tank fuel pump operating restrictions (low fuel levels and the pump goes off). Why were they only recently introduced and what is the 'fix' to allow some AB ac to fly unrestricted? Are the problems related to the electrical wiring of the pumps, or is there some other reason?

Thanks, your help is appreciated,

Flipster

nosewheelfirst
20th Jun 2006, 18:00
On the a320 series its down to a screw's torque not being checked when fitted.

BOAC
20th Jun 2006, 18:07
I believe it followed the 747 crash off the US coast a while back and a ground explosion in a 747 centre tank. The implication/diagnosis was that the pumps had overheated or wiring had shorted causing the problems, so it was arranged to turn them off as a 'normal' procedure while they still had fuel coverage in the tanks. They can of course, be run to empty if the fuel situation requires it and the scavenge system normally takes care of using up the remaining fuel.

As I understand it the 'fix' involves modified pumps.

tired
20th Jun 2006, 19:28
No restrictions on A343 and 346

PhilM
20th Jun 2006, 20:27
As I heard it, its due to the 747 explosion that happened (mentioned above), with a wiring/fuel pump fault in the centre tank.

The problem comes I believe when you have little quantities of fuel in the centre tank, the air fuel mixture is apparently good for an explosion, if there were to be a re-occourance in the wiring fault/pump fault.

To counter this, were told when fueling aircraft, when the centre tank is to contain any fuel, it must be a minimum of 2 tons. (Above the critical AFR).

If we have an AC with a wing capacity of 6tons/wing. And we were going flying with 13 tons of fuel to our destination, we cannot have full wings and one ton in the centre.

We would pre-load the centre with 2 tons, and then put 5.5 tons in each of the wings.

Check Airman
20th Jun 2006, 22:22
I believe it followed the 747 crash off the US coast a while back and a ground explosion in a 747 centre tank. The implication/diagnosis was that the pumps had overheated or wiring had shorted causing the problems, so it was arranged to turn them off as a 'normal' procedure while they still had fuel coverage in the tanks. They can of course, be run to empty if the fuel situation requires it and the scavenge system normally takes care of using up the remaining fuel.

As I understand it the 'fix' involves modified pumps.

I believe the rationalle is the same for the 767

flipster
20th Jun 2006, 22:26
Yes, the thought of fuel/air mix and sparking pumps does not fill me with joy! I believe this is the reasoning behind the Boeing restrictions.

However, if the AB restrictions apply because of the torque of screws/bolts, why can you put some fuel in the centre tank (A320/319 - >2000kg, IIRC) - and that's ok but when you get lower than this - the fuel becomes 'un-useable' and the pumps must be switched off???

This seems strange - or is it that if the torque on the pump screws/bolts is less than ideal, then this could lead to sparking/fire/explosion. (Above 2000 kg, the pumps would be definitely covered in fuel, any less and the pumps may become uncovered, coming into contact with the ullage (fuel air mixture))?

Whatever the reason, I don't quite follow the logic of AB - we've just been given a temp procedure but without any adequate (IMO) explanation as to why.

FlightDetent
21st Jun 2006, 13:51
Read the OEB and you will see. There is full page.

On a certain type of pump screw was found loose.

This "cause the pump's internal flame trap to be uncovered".

Under such scenario, the separation of pump's electrical components from fuel-air mixture cannot be guaranteed.

Adopt the procedure to run the pumps only fully covered in fuel. All pumps off for refuelling. Center pumps of when less than 2t.


If you do not read the OEB, or you are not provided with it, it is hardly Airbus fault.

FD.
(the un-real)
To say that center tank fuel below 2 tons is unusable is simplification.

flipster
21st Jun 2006, 14:32
Thanks FD,

The prob is we haven't yet got to see the actual AB OEB/TR (if we ever do) - all I have seen is the Notice to Crew which is airline specific - our SOPs are slightly different from the AB generic - but are AB approved.

However, I have also discovered that if torque of the pump screws in question was not enough, then there is a risk of fire/explosion in the tanks, as you say. Nonethless, I agree the TR should stop that happening and the AB pumps are different from Boeing ones so there is very little risk. In the meantime, inspections are being carried out rapidly, allowing most of our ac to fly unrestricted!

BUT.......fuel and fire fills me with a little dread - TWA 800 and all that! I believe that risk assessors think such a thing is very unlikely to happen - only one occurrence every 2 years, so its not worth the modification! Hmmmm - try telling that to the relatives of TWA 800!?

This is a good read:

http://en.wikipedia.org/wiki/Inerting_system

Perhaps, instead we should be asking for fuel inerting systems to be employed as a matter of urgency to all our ac - this fuel pump problem could then be easily solved - for ever. Military ac have inerting systems because people fire at them and their risk is a lot higher - we, however, are at the mercy of our own ac.

(BTW - not all military ac get such protection as inerting sytems or explosive suppressant foam - a bit of a problem for these guys and gals

see http://www.pprune.org/forums/showthread.php?t=215665

World of Tweed
21st Jun 2006, 18:17
What is puzzling though is that in my company the Pumps in the CTR tanks have been modified and all the work completed nearly 18months ago. In theory we are able to run them dry quite happily according to highly reliable engineering Gossip i.e. one of the guys who embodied the mod.

And yet our CTR Tank restictions are still in place. Any one else have a similar situation?

gas path
21st Jun 2006, 18:59
world of tweed
All the fuel pumps, boost and Jett o/ride, were modified from Crane Hydro-aire to FR-hitemp. with the complete embodiment of the SB all the restrictions on pump usage were removed.
Maybe you still have one or two a/c awaiting full embodiment:confused:
Interestingly enough the NTSB investigation found the Crane pumps to not be at fault, rather pointing the finger at a wiring short outside of the tank that allowed a 'high voltage/current' to enter via the fuel qty. measuring system.