Hi to all people,I'm trying to understand how to insert properly the figure of Reserve Fuel in the FMC.Specifically I use 737-800 PMDG (but this is the same for all aircraft with FMC) and FSBuild for fuel and flight planning.The RESERVE FUEL value to insert in FMC is the result of RESERVE FUEL + ALTN FUEL or only RESERVE FUEL?737-800 PMDG Manual Fuel planning tells that RESERVE FUEL infact the result of RESERVE FUEL + ALTN FUEL, but it's not logical. Because if you divert from your destination airport to an alternate you are infact in low fuel condition and INSUFFICIENT FUEL warning message, correct?Thanks

My understanding is that you input the minimum amount you want to (and can legally) land with. A diversion should not cause the "Insufficient Fuel" message.

That is computed relative to your actual 'alternate' airport, which I doubt most people flying FS actually figure in. It is a legal requirement in the 'real world':Sec. 91.167 - Fuel requirements for flight in IFR conditions. (a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to -- (1) Complete the flight to the first airport of intended landing; (2) Except as provided in paragraph B of this section, fly from that airport to the alternate airport; and (3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.

Thank you guys for replies, sincerely I'm in agreement with trisager. In fact FSBuild give you various fields:TAXI ......DEST TO AIRPORT ......RESV .......ALTN .......HOLD .......EXTRA .......TTL AT TO .......REQD .......I think you must insert in FMC field the RESV fuel value (in kgs or lbs) like "minimum amount you want to (and can legally) land with" and not ALTN+RESV. Infact suppose you fly from A to B and C is your alternate. Suppose for many reasons you cannot land in B after one or two approaches, so you must divert to C (and thus your are using allready your ALTN fuel), now you are UNDER your minimum amount you want to (and can legally) land with, because your are using ALTN fuel to go to alternate airport, so you cannot land with this minimun required fuel.So I think it's correct to insert only the RESV field and this this amount is generally fixed for every aicraft, in my specific situation is 45mins or 1800 libs.What do you think about?