ATC and reserve fuel

>So a hold even if it is not part of the arrival proceedure is>an expected delay ((:( Anticipated traffic delays) or would>that only be expected if dispatch/ATC told the pilot prior to>or during flight?on a release it will split the fuel into categories, for example at my airline you would see: ARPT FUEL TIME DIST DEPT DFW ENRT LBB 002467 0050 0251 --------------------------------------------------------------- RSV 01700 0045 CAPT ADD 00100 0003 BUFR 00100 DISP ADD 00600 0020 BUFR 00300 ALTN MAF 01108 0024 0105 HOLD 00433 0015 MEL/CDL 00200 0006 --------------------------------------------------------------- T/O FUEL 006608 MIN T/O 006208 --------------------------------------------------------------- TAXI 00408 0017 ------ TOTAL 007016 so from DFW to LBB you are expecting a fuel burn of 2467 lbs which is 50 min for 251nm.the 45 min RSV is 1700lbs. the ADD fuels are additional fuel the CA or dispatcher has added and 100% of the CA and 50% of the DISP have gone to the bottom line (ie you have an additional 300lbs to play with on taxiing) however in reality the BUFR % is 25% as a default. for MAF the ALT fuel is 1108lbs which is 24 minutes, 105nm, from LBB. the dispatcher has given the CA 433lbs, 15 minutes, of holding fuel because they think a delay may occur. there is also 200lbs of fuel added for an applicable MEL/CDL (for example a wing seal may be missing requiring a 2% increase in fuel burn). adding all of this up gives you a T/O fuel of 6608lbs. your absolute minimum T/O is 6208lbs (this is the number you have to have when wheels up), however there is still 300lbs of DISP ADD fuel that could still be buffered, so the real number is 5908 but if you need the 300lbs this release would have to be amended showing that extra 300 being taken out (a pen and ink correction). you then simply add the 408lbs of taxi fuel to this to get the TOTAL fuel which is the amount of gas the fueler will put on the airplane at the gate.the fuel requirements are a T/O amount regulation. you DO NOT need to land with 45 minutes of fuel, plus the alternate fuel. each CA has their personal mins (a common one is the 45 min reserve plus a small amount say 500lbs) and use various techniques at their disposal. if they are holding, they will coordinate with dispatch to find an appropriate diversion airport (just because an airport is listed as your alternate doesn't mean you have to use it as your alternate and ATC has no idea who you're alternate is).a good example could be you are holding 40nm away from ORD with 5000lbs of gas. you coordinate with dispatch and they tell you a lot of airplanes have already gone to your listed ALT of FWA so they would prefer you to goto IND. the CA's personal safe zone is 2500lbs of gas and from your present position you are 1000lbs of fuel burn away from IND. based on this he will hold until they have 3500lbs of gas, at which point they would divert to IND. of course each carrier is different and might even mandate the RSV requirement plus burn to diversion as an absolute minimum.hope this helps.