Originally Posted by
320ToBearz
in general, you get to your reserve of 45 minutes of fuel in a light ifr or vfr day, then you divert.
Just to be on the safe side, I think you had better start that divert sooner.
For Part 121 jet ops, you'll need to plan to divert with fuel enough to get to the divert location and then have 45 minutes of fuel on board. The 45 minutes of fuel is what you plan to land with...not when you start the divert.
For Fire...
Figure out what a typical fuel burn number is for your airplane when holding...figure it for 'x' amount of fuel per minute. That value will allow you to easily figure your burn while holding.
Then figure out a typical burn (in 'x' amount per minute) for cruise...the cruise, for example, that you would use when diverting from a hold to a divert/alternate. Figure out your average ground speed in miles per minute in this divert cruise (no wind). Compute the divert distance, divide this by your estimated cruise ground speed in minutes. This gives you ETE to the divert/alternate (no descent planned just to be conservative). Then multiply the ETE times your cruise burn rate to get the estimated enroute burn. Add your FAA reserve fuel to this value to arrive at the divert fuel.
For example:
Cruise burn = 100#/minute. Cruise ground speed (no wind) = 4nm/minute.
Distance from the hold to the divert/alternate = 100nm.
ETE = 100 divided by 4 = 25 minutes.
Cruise burn = 25 minutes X 100#/min = 2500#.
If your reserve was 3000#, then your divert fuel = 3000# + 2500# = 5500#.
Now, let's say your estimated holding burn was also 100#/min. You are in the hold with 7500# remaining. You want to divert at 5500#. You have 2000# to burn in the hold...at 100#/min, this equals 20 minutes of holding time before you divert.
Maybe others can add their techniques!