×
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.

I just came across this question in Exercise 1.5 in perfomance book.
The pressure height is -270.
The ISA temperature what I thought was 15+(2*0.25).
But the ISA temp was calculated as 15+2*0.5
I am a bit confused here. Can you please help me get around this. Screenshot attached.

bobtait replied the topic: BT book exercise question

Also, referring to your original question. There has to be a limit to the degree of interpolation in these situations. I'm sure even CASA would agree. 1 hPa for every 30ft is itself an approximation so the calculated pressure height of -270ft is not likely to be exact. We do encourage students to use the calculation (flow chart) method for an exam because it eliminates the possibility of misreading a scale on the computer and it's just as time efficient. CASA accept an answer based on a flight computer which would be nowhere near that level of accuracy.

Surely, we are not going to start working with fractions of degrees of temperature. Based on the assumption of 2° per 1000ft temperature lapse rate, -270ft could be rounded up to the nearest 500ft to give an answer of 15 - 1 = 16°. Even CASA accept that.