Ctr fuel pump restriction on GND, 737NG
Hey guys
How come you may empty the center tank fuel while in the air but not on the ground? On the ground you have a restriction of 453 kgs (1000 Lbs) to turn the pumps on before startup. Then you'd have to turn them off again before T/O, but that I understand. Any good answers? |
nuisance/distracting master caution on take off?
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Is this a new limitation? I was not aware of it in 2008. I'm sure you can run them for defuelling or fuel transfer. Otherwise as the bus says. They would almost certainly illuminate on take-off at that state.
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Yes, new since last update
But since 2008 there have been a number of special procedures with the 737 fuel systmem We operated them under a AMOC for a long time. |
How come you may empty the center tank fuel while in the air but not on the ground? |
It is a cooling matter.
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It is a cooling matter Here's the link: Thai 737-400 Fuel Tank Explosion - 3 Mar 2001 |
Since then a few things have changed. Center tank fuel pumps will switch themselves off if output pressure is low (after a short delay) and airplanes have an NGS fitted.
I would think it is a cooling matter indeed, the explosion risk of dry running pumps has been fixed. |
Do any of you guys have any document references?
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I'm pretty sure the 'cooling thing' is a red herring since I understand the NG wing pumps are in the centre tank too, so that would make committing any form of aviation in an NG with an empty Ctre tank somewhat difficult:)
I would have expected EITHER the AFM un-modded pump restrictions (2300kg) OR NO restriction for modded pumps. I remain convinced that (if it is not an editing error) it is to prevent 'nuisance' alerts. |
Yep...BOAC, you're right, all the main and centre fuel boost pumps are physically located in the centre tank space. But that has no effect on running the main tank pumps because they will be cooled by the fuel they are drawing from the main tanks 1 and 2.
Unlike the centre tank pumps, which would not be cooled at all when the centre tank runs dry. Cheers..EW73 |
Thanks for that, EW, but I would have thought with 'modded pumps' the problem of 'cooling' would not arise since they shut off or would be shut-off by crew, or have I misunderstood the mod?
My understanding of the AD was ''Center Tank Fuel Pumps Intentional dry running of a center tank fuel pump (low pressure light illuminated) is prohibited.'' and that the 'no ground running <453kg' was only listed as an alternative means of compliance so the primary compliance should be ok? |
In the 732 the wing pumps are in dry bays in the bottom of the wing, thus allowing for their removal without defuelling the wing tanks. The centre tank pumps are in the leading edge of the wing, for the same reason. Has this changed in the NG?
The min fuel requirement for running the centre tank pumps is, I suspect, to avoid the possibility of the tank being run dry and the pump overheating - the suspected cause of the explosions in the centre tank on the ground. In the air, one is encouraged to turn the pumps OFF as soon as the low pressure light illuminates. |
Schiller - see #10, #12 and #13
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Running dry can't happen anymore as the pump switch themselves off. Apart from that there is no combustible gas mixture inside the centre tank since the nitrogen generation system fills the center tank with mostly nitrogen, not completely, but oxygen is well below below the required level. Apart from that, yes, center tank pumps have to be switched off manually when the low pressure light (and master caution) comes, not only in the air but on the ground as well of course.
Unmodded airplanes have somewhat different limitations, they should have a placard with those in the field of view of the operating crew inside the flightdeck. Kinda interesting, the 453kgs limitation is only found in the the cockpit preparation part of our manual, it is not listed in the limitations part. |
If the position of the pumps in the NG is different from the 732, why the change? Does anyone know? It seems odd to move them to a position which makes maintainance more difficult.
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Center Tank Pumps
How come you may empty the center tank fuel while in the air but not on the ground? running the center fuel tank pump with low fuel level in the tank has been a concern. |
Into what or where would you PUMP the center tank fuel while on ground ? |
Originally Posted by gg
Into what or where would you PUMP the center tank fuel while on ground ?
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I guess the difference in "ground" and "air" limitation exists because in the air fuel is cooler than on the ground, so running the CTR pumps with less than 453 Kgs in flight is not as dangerous as running them on the ground.
Kinda interesting, the 453kgs limitation is only found in the the cockpit preparation part of our manual, it is not listed in the limitations part. |
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