ATPL flight planning question

[xxRED BARONxx]

Hey guys, just a quick question (not too complicated), I was just wondering if when using the TAS equation (True mach no. x 39 x square root of true temp+273) you should use 38.975 or 39 (for simplicity) in the equation??

I know its not much difference at all but Ive done a few calcs and found the TAS to be 1-2 knots different when using 39 or 38.975 which got me wondering if I used one or the other in a 5 mark question it would alter the answer enough to get two different answers in the CASA exam (I dont know how spaced each answer is).

What did you guys use??

thanks

[CazbahKid]

39 is fine for the exam.

[muffman]

39 will lead to the answers they have supplied. Anything other than that may actually leave you with an answer that's between two of their options.

Also, be careful not to fall into the trap of attempting to be unnecessarily precise with your calculations. The rounding and interpolation principles are available on the CASA website and you need to stick to these. Sometimes, people try to leave all the rounding until the end. It is more precise, but it is not the way the CASA answers were produced.

[training wheels]

.. and after you've done the exam, you'll probably never ever use that formula again. :E

[Phot]

I did the exam a few months ago and didn't use it at all.