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MartijnPleines

Dry center tank flameout problems?

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my question is...should we allow ourselves to run the center tanks dry at all?From what I've read (Bulfer FMC guide and, in particular, the link below) at least 1000 lbs of fuel should be left in the center tanks to keep the pumps submerged to avoid a explosion/fire risk (sparks igniting the fumes-it seems to have happened to Boeing aircraft on a number of occasions)?http://www.b737.org.uk/faaad.htm-takeoff: switch center tank pumps off if <5000lbs-clb/crz: switch center tank pumps off if <1000lbs-des/ldg: switch center tank pumps off if <3000lbsRegards,Martijn

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Hi Martijn, I recently sat in the flight deck during a flight using the -800 version. I explicitly asked the captain the same question as I noted that they allowed the center tank to run dry. He said that Boeing had changed the procedure after the TWA800 (can't remember the flight number right now, but it was the B747 from TWA that exploded in 1996 shortly after takeoff from JFK). The procedure they used was to let the center tank run down until approx. 1000 lbs and then switching on cross feed and turning off one of the fuel pumps. In this configuration the center tank is allowed to run dry. After this happens, the remaining fuel pump is turned off and cross feed is closed again.Hope this helps, :-waveBoaz

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OK, cool.My point was that we might avoid the flameout problem by adhering to RW procedures. I just tried out the procedures you described and did not get any flameouts-even when I 'forgot' to execute the latter part (switching off the remaining fuel pump and crossfeed as the tank ran dry) :-cool Still a bit puzzled since it would not help avoid the (RW) condition where a spark from a working fuel pump might ignite the fumes in a dry tank. Might I ask...what airline was that? ;-) Edit: Cheers,Martijn

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Hi Martijn, Admitted I am in no way a real world pilot, but I seem to remember that the center tank fuel pumps work at higher pressure than the wing tank pumps making sure that the center tank is depleted first if all tanks have fuel (EDIT: and the pumps switched on). Therefore I would not think that you would get a flame out if you forgot to switch off the remaining center tank fuel pump. Maybe a real wold 737 driver would care to comment on this?With regardsBoaz

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BoazYou are correct in your understanding of the Center Bosst pumps overiding the main tank pumps when both are operating. The reason behind the AD that required leaving 1000lbs of fuel in the center tank had to do with repair shop findings on several removed boost pumps. Several pumps were found to evidence of overheating (blueing of the metal) and wire damage inside the pumps. To avoid any possibilty of trouble Boeing required all operators to remove the pumps and verify the wire routing in the pumps via X-ray. They then placed the restriction on the the affected fleets of airraft that the pumps must be shut off with 1000 lbs of fuel in the tanks to avoid running the tanks in a fuel vapor enviroment without cooling (fuel). So the latest real world procedures for all 737 600 thru 900, 757 and 747 operators (according to the AD paperwork) is that if center tank fuel is required, a minimum fuel load of between 2000-5000 is required and the pumps must be shut off at 1000 lbs. Hope this helps explain the reasoning behind thisRegardsPaul Gollnick :-coolTechnical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.com

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I'm not a RW pilot either (as you might have guessed)-but there's an issue with the PMDG flaming out the engines when the center tank is allowed to run dry with both pumps on, isn't there?-see one of the anchored posts near the top-I decided to post outside of that thread since my suggestions did not address the issue directly.So that's the problem I was referring to-and the fact that we can simply avoid the matter by either switching off both fuel pumps early according the procedure alluded to in my original post, or using the procedure you mentioned in your post.When I mentioned the fact that I didn't get a flame-out when I 'forgot' (deliberately to test it) to switch off the remaining pump and xfeed I did not mean to imply that I thought that I should have had a flame-out. I just wanted to make sure that the issue with the flame-outs did NOT occur in this situation too, and it didn't.So I am happy with the whole procedure as it is. Hope I'm not causing too much confusion here...I'm simply having a lot of fun researching this thing and am delighted at how well the PMDG 737 reacts if you try to follow RW procedures.Thanks, Martijn

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Just experienced my very first flameout under FS9. Only lost the right engine so it was a minor flip panel and inflight restart ;)Just curious, this seems to really be a time slice issue, since the engines alternate stealing fuel to simulate multi-tank pumps and stuff due to single source logic in FS, perhaps there is a minor glitch in the check for fuel logic? ie: it checks for fuel, sees fuel, engine one drinks, engine two drinks, checks for fuel, etc...Perhaps just based on timing, the check passes, engine one drinks, engine two whoops! engine one stole my fuel :-lolFlameout!As I have only seen this once in many flights and I have deliberately been running with 1% in center tank at start of all flight just to try and make it happen, perhaps we can just change the FUEL caution alert to trigger on at the 1000 left in center instead of the 0 left in center level?

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A really easy way for the programmers to fix this is to program the center tank fuel gauge to report 0 lbs when fuel is less than 100 lbs, and "transfer" fuel from the selected main tank(s) to the center tank to keep the center tank fuel level at around 75 lbs. By transfer, I mean decrement the main tank levels and increment the center tank level by the corresponding amount. The tank would appear empty, but will never actually reach 0 and flame out the engines unless the main tanks have run out of fuel to transfer.RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, D.C.

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