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Guest rcarlson123

Question on fuel loading requirements

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In one of the threads related to my fuel planner utility, someone mentioned that most airlines have a standard procedure to load 1000 pounds of fuel in the center tank at all times. I'm wondering if anyone can verify that, and if that's more than just an airline SOP, like if it's recommended by Boeing. I would like to modify my fuel planner utility accordingly.(BTW, I know of the separate requirement that you need to have the wing tanks full if you have 1000 pounds or more of fuel in the center tank.)Any input would be appreciated!

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I hate to bump my own threads ... but I was really hoping someone had some information on this subject. Anyone have any pointers? Perhaps URLs where I could do more research?

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Don't have any URL's or anywhere you can read about it. The only thing I remember about was that they do this so that the tanks aren't comletely dry, and to keep some fuel in "the system" of the main tanks. I guess your tubes and stuff could freeze up or something if completely dry...I don't know.Mikkel

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Hey Ross,I believe it was me that mentioned that before. I can't remember the exact reason, but I believe it was to keep the pumps submerged. I think unsubmerged pumps had a tendency to spark and cause a fire? Probably best to let one of the real NG drivers answer, but I will do a bit more research on the subject as well.Take care,JeffEDIT: Found this...http://www.airweb.faa.gov/Regulatory_and_G...6E?OpenDocument---------------------------------------Airworthiness DirectiveRegulatory Information2002-19-52 Boeing: Amendment 39-12900. Docket 2002-NM-249-AD. Supersedes Emergency AD 2002-18-52. Applicability: All Model 737-600, -700, -700C, "800, and -900; 747; and 757 series airplanes; certificated in any category. Note 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (l)(1) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. Compliance: Required as indicated, unless accomplished previously. To prevent fuel vapors from coming into contact with an ignition source in the center wing fuel tank, horizontal stabilizer fuel tank, center auxiliary fuel tank, or auxiliary fuel tanks 1 and 4, which could result in fire/explosion, accomplish the following: Revision of Airplane Flight Manual (AFM): Model 737-600, -700, -700C, "800, and -900 (a) For Model 737-600, -700, -700C, "800, and -900 series airplanes: Within 14 days after the effective date of this AD, concurrently perform the actions required by paragraphs (a)(1) and (a)(2) of this AD: (1) Remove the AFM revision required by paragraph (a) of emergency AD 2002-18-52; and (2) Revise the Limitations section of the FAA-approved AFM to include the following (this may be accomplished by inserting a copy of this AD into the AFM): "Certificate Limitations The center tank fuel pumps must be OFF for takeoff if center tank fuel is less than 5,000 pounds (2,300 kilograms) with the airplane readied for initial taxi. Both center tank fuel pump switches must be selected OFF when center tank fuel quantity reaches approximately 1,000 pounds (500 kilograms) during climb and cruise or 3,000 pounds (1,400 kilograms) during descent and landing. The fuel pumps must be positioned OFF at the first indication of fuel pump low pressure. The CWT fuel quantity indication system must be operative to dispatch with CWT mission fuel. Note The CONFIG indicator will annunciate when center tank fuel exceeds 1,600 pounds (800 kilograms) and the center tank fuel pump switches are OFF. Do not accomplish the CONFIG non-normal procedure prior to or during takeoff with less than 5,000 pounds (2,300 kilograms) of center tank fuel or during descent and landing with less than 3,000 pounds (1,400 kilograms) of center tank fuel. Note In a low fuel situation, both center tank pumps may be selected ON and all center tank fuel may be used. If the main tanks are not full, the zero fuel gross weight of the airplane plus the weight of center tank fuel may exceed the maximum zero fuel gross weight by up to 5,000 pounds (2,300 kilograms) for takeoff, climb and cruise and up to 3,000 pounds (1,400 kilograms) for descent and landing, provided that the effects of balance (CG) have been considered. If a center tank fuel pump fails with fuel in the center tank, accomplish the FUEL PUMP LOW PRESSURE non-normal procedure. When defueling center or main wing tanks, the Fuel Pump Low Pressure indication lights must be monitored and the fuel pumps positioned to OFF at the first indication of fuel pump low pressure. Defueling with passengers on board is prohibited. The limitations contained in this AD supersede any conflicting basic airplane flight manual limitations."

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Hrm ... not sure what to make of all that. :) But I think I will modify my fuel planner so that it always loads the first 1000 pounds of fuel into the center tank, then fills the wing tanks, then continues filling the center tank.Thanks for your help!

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Hey Ross,Sorry for posting the whole article. I really only did it for overall context. Here is the important part... ;)-----------------------The center tank fuel pumps must be OFF for takeoff if center tank fuel is less than 5,000 pounds (2,300 kilograms) with the airplane readied for initial taxi. Both center tank fuel pump switches must be selected OFF when center tank fuel quantity reaches approximately 1,000 pounds (500 kilograms) during climb and cruise or 3,000 pounds (1,400 kilograms) during descent and landing. The fuel pumps must be positioned OFF at the first indication of fuel pump low pressure.------------------------I would assume in your calculations that this fuel would be considered ballast weight and thus added to the ZFW for all of your computations.Good luck and thanks for all of the hard work!Jeff

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Hrm, not sure about that. The documentation that came with the plane (the cruise planning chapter) states that ZFW is the basic operating weight of the aircraft plus payload (pax, baggage, cargo.) I don't think ZFW should include any fuel at all, but I'm not sure.Really all I want to know is if there should always be at least 1000 pounds of fuel in the center tank when the aircraft is fueled before flight, even if those 1000 pounds aren't needed for the flight or reserves. I've seen it mentioned a few times that the center tank should have 1000 pounds in it to keep the pumps submerged, in order to prevent vapor combustion if there is a spark in the pump.The text you pasted above states that the pumps should be shut off at 1000 pounds during climb, or 3000 during descent (strange that the descent number is higher...) so that jives with the "keep the tanks submerged" thing.I think I'll go with that and modify my fuel utility so that it always puts 1000 pounds in the center tank before filling the wing tanks.Thanks for all the help!

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>Hrm, not sure about that. The documentation that came with>the plane (the cruise planning chapter) states that ZFW is the>basic operating weight of the aircraft plus payload (pax,>baggage, cargo.) I don't think ZFW should include any fuel at>all, but I'm not sure.>>Really all I want to know is if there should always be at>least 1000 pounds of fuel in the center tank when the aircraft>is fueled before flight, even if those 1000 pounds aren't>needed for the flight or reserves. I've seen it mentioned a>few times that the center tank should have 1000 pounds in it>to keep the pumps submerged, in order to prevent vapor>combustion if there is a spark in the pump.You are correct in assuming that the ZFW does NOT include any fuel remaining in tanks. This fuel becomes a part of the fuel load after servicing, and thus to all intents and purposes is non-existant when calculating the ZFW.Steve MRetired Dispatcher, Load Controller and general dogsbody :)

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Hey Steve,I definately see your point about this fuel not being a part of the ZFW. But, since this fuel is really NEVER supposed to be used, why wouldn't it then be considered ballast? It seems this additional weight would be treated the same as extra payload. I think I remember reading something like this in one of Bill Bulfer's manuals on the NG.Take care,Jeff

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Maybe because you are allowed to use it in a minimum fuel situation. Not sure, just guessing here.

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