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Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
So I recently sat the CFPA exam again for the 2nd time and a few things which struck me was one question along the lines of;
Alpha to bravo to charlie (alternate)
435L at start up
388NM @ 310M A to B
Fuel flow 92/hr
Had a tempo at the departure and an inter at the alternate
Wind was a 30k pure cross wind (so ETAS was 139kt )
Anyways I assumed you would work this question out by first finding the safe endurance (435L - taxi - fixed - holding(for 1hr)) / 1.10 - Alternate fuel = Safe endurance fuel (since according BT textbook when working out you always assume the Alternate doesn't need a variable/fixed reserve?). Now I am fairly certain I got this question wrong because it showed up on my KDR about PNRs but there were multiple questions but I wanted to know if I was missing anything important for this in terms of the order of determining how much fuel would be left for safe endurance?
If you are calculating a PNR, the original flight planned trip has nothing to do with it. All that matters is how much of the total fuel on board can can you plan to burn on the way to the PNR and back to the departure aerodrome. The only holding you have to consider is the holding at the departure aerodrome because that is your destination as far as the PNR is concerned. Also, you don't have to take out the alternate fuel since if you do decide to return from the PNR you wont be going to the alternate.
Thank you so much for clearing this up Bob! I think where I got confused was treating it like a minimum flight fuel calculation (ie, adding everything in). For the sake of my own workings out I will probably treat it like this when calculating PNR's (correct me if I am wrong).
(Startup fuel - Taxi - Fixed - Departure Holding (if applicable)) / 1.10 - Alternate (if applicable) = Trip fuel; Then just adding the Alternate back on to = Safe Endurance for PNR!
And lastly while I have your ear Bob! Can you clarify for me that in the PNR calculation in regards to ETAS it would look like the following with no headwind applied - Safe endurance X ETAS home / 2 x TAS or would it be 2x ETAS on the bottom?
I wonder if you have to apply the 10% variable reserve on the holding fuel?
As Bob says in his book:
"Because holding fuel is used AFTER the flight has been completed. it is NOT trip fuel" ..., and then comes the calculation on page 101 which explicitly express that the 60 min holding (at 17,2 gph) is NOT calculated with the 10% variable.
I hope it will be of help!
*PS it would be great to know all data of the problem, I'd give it a try to solve it!