Hi

I was reading in another part of a forum and it was quoted as FR was calculated as used (subtracted) from remaining fuel left if you were to hold at another destination... it had me super confused, can someone please clarify the below scenaro.

Lets say Casa asks:

Fly from A to B, due to B unusable how long after flying to C, can you hold there?

I can figure out all the maths from distance/time/speed/fuel burnt ect I'm just wondering what is remaining?

I assume from

Cruise
Alt (n/a)
VR
FR
Hold (n/a)
Taxi
TOTAL

Assuming there was no Alt or Holding fuel required and you had full tanks.

So far you have used your Taxi and your portion of fuel used to fly to the destination.

Do you assume you have used your VR and all you have remaining to, say hold, is your margin of fuel remaining flying from A to B to C and your FR?

Or do you assume your VR wasn't used and that is also available to add to your holding time?

Thanks

Jason.

Fly from A to B, due to B unusable how long after flying to C, can you hold there?

It all depends on where you do the calculation ..

(a) preflight - you have to fly A-B then divert B-C. Presuming you don't dilly dally at B, you can plan on having at C

full tanks - (start/taxy at A + planned fuel burn A-B- (overhead) C + approach and landing C + VR A-B-C + any requirements C + FR) available as margin fuel when you get to C for whatever you might choose .. for your concern, holding. Note that you must plan on using all the VR as you have no definite way of knowing how much of it you will use for this particular flight. Obviously, you would expect not to use all of it and pick up some extra holding as a result when you get to C and reassess the situation for holding ...

(b) if you replan overhead B you will have

fuel total overhead B = full tanks - actual burn from start A to overhead B available to cover the rest of the flight .. which leaves, for holding at C

fuel total overhead B - (planned fuel burn B - (overhead) C + approach and landing C + VR B-C + any requirements C + FR) available as margin fuel when you get to C .. which you can apply to holding. Normally you would expect to have made some fuel during the segment A-B which should give you more holding that you had planned for preflight. This strategy is what you are doing when you don't have quite enough fuel at departure for your flight - so plan to a PNR with the expectation that you will make enough fuel to replan through to the destination rather than go PNR.

(c) if you reassess overhead C, you go through a similar exercise, having an expectation that you will have made up some more fuel during the segment B-C which would, normally, give you a bit more holding time at C.

Normally you would expect to have made some fuel during the segment A-B which should give you more holding that you had planned for preflight.
This is very true, but in the real world of GA how does one go about calculating the reserve fuel released for holding? Its not as if the pilot can dip the tanks in flight to determine how much fuel has been consumed.

Draft CAAP 234-1(2) sums up the above (John's) statement nicely - sorry but par 5.3.3 was split over two pdf pages

in the real world of GA how does one go about calculating the reserve fuel released for holding?

Very cogent point.

However,

(a) if one has a debimeter or similar, one is in front

(b) even an accurately known (ie generally dipped) pre-start quantity plus known consumption rates against the clock and the flight log, with a gross check against contents gauges ... will provide a reasonable starting point.

Much easier on big iron ..

Harold's story makes for riveting reading.

Another case I recall involved one of the airline's flight standards bosses in the left seat .. PER-MEL, as I recall .. didn't end up too promising at MEL .. eventually a very close unplanned diversion to CBR and the noises started stopping on the taxy in to the terminal.

A more recent 737 case involving two aircraft can be reviewed here - www.atsb.gov.au/publications/investigati...13/aair/ao-2013-100/.

Historically, Australia is a right mongrel for unforecast fog, especially during the winter months. I have never been caught out to the degree of the cited stories but, on a number of occasions, we had sweaty palms running and re-running the fuel calculations in flight.