phil@LFPG
25th Sep 2005, 18:47
hello,
i was wondering why decompression fuel and distance is calculated for twins (etops) with 10 000' and for three or four engines at 14 000' ???!!!!
any help or thoughts ???!!!
phil
Hi,
Haven't done ETOPS planning in a long time but seem to remember that we are looking at the "Critical Fuel" required over and above "Normal Fuel Reserves". At 10K, fuel burn on 1 at MCT is higher than at 14K. There is of course the requirement to take "Icing" into account. "Touchy subject." I seem to recall that AC120-42A is the document to look at.
There was once a huge debate with ETOPS Operators and the Vendors of Flight Plnning sysytems as how to compute the "Crit Fuel". Some use the BANG Down to 10K without drift down calculation, others compute the drift down Time/Fuel/Distance. I am a conservative. Bang down and start the calculations without drift down. Give the pilots a bit of an edge whilst they fly a drift down profile.
Thats my 2 cents
Cheers