Regarding this 480kt vs 450kt wierdness:
https://i.gyazo.com/0401a1f0cda2db36...7f0ffe4008.png
I put the question's numbers in the system, and TAS is indeed given as 480kt.
And, if you compute EAS/CAS, you will find 0.94.
So, the best I can come up with to explain the whole situation is that they made a mistake in thinking the compressibility correction should be applied to the TAS whereas it should be applied to the CAS only.
A situation where the correct answer would be 450kt is the following :
Mach number is measured from (Pt-Ps)/Ps.
So, say you don't have any device to correct your machmeter for compressibility (which is a problem in itself.. but let's assume that).
The machmeter will overread, due to compressibility.
Let's see how it will overread in details :
You are flying at 450 KTAS (but don't know it yet)
You measure Pt, and find you're flying at 265 KCAS (and 252KEAS in reality)
However, since you're measuring a Pt that's higher than the real one, you're actually not accounting for compressibility, and whereas your EAS is 252kt, you mistakenly believe you have an EAS of 265kt
When you correct for density to get TAS, you compute TAS from an EAS that's higher than the real one, so TAS is higher than your real TAS, close to 480kt.
Then you compute your mach number and find a number close to 0.8.
So you believe you're flying at M0.8
Your machmeter measures M0.8, but it actually overread due to non accounting of compressibility.
At this precise moment, you're in your imaginary aircraft with your wierdo-non-corrected-machmeter and an EASA civil servant steps into the cockpit and asserts the compressibility factor is 0.94. Darn, your non-corrected-machmeter overestimated speed by a factor of 6% !
So you're flying at M.75, which is exactly 450kt.
I reckon it is very very far fetched and I don't know what I would answer if this question did come up.
I don't even know if a non corrected machmeter exists...
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