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Thread: ATPL Flight Planning Tricks, Short Cuts etc
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Old 16th Apr 2018, 09:02
  #289 (permalink)  
FLGOFF
 
Join Date: Oct 2011
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Originally Posted by Starjkd
Hi have been reading both AFT and Rob Avery and now am pretty confused.

Rob Avery seems to mention all ISA deviations need to be rounded to multiples of 3 for both fuel flow AND TAS... however in the casa atpl booklet and from what I've learnt form AFT it only mentions to do this for the fuel flows.. what does everyone else do for the Tas?
Thanks in advance
AFT use the speed of sound formula instead. The ISA deviation is accounted for in the OAT in the formula.

TAS= √(273-OAT°C)*39*M-1

E.g FL350, 0.82M, ISA+4

[√(273-50)]*(39*0.82)-1=477KTAS

Rob's method uses the published TAS in the POH accounted for ISA deviation instead of using the formula.
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