Part 25 altimeter accuracy
I just got asked an interesting question by a curious meteorologist, haven't a clue of the answer, but hopefully somebody here might know?
As we probably all know, altimeters on non RVSM compliant part 25 aeroplanes have to be accurate to ±30ft per 100kts.
Question is - what's that 100kts in? Part 25 just says "speed". I'm guessing is that it is either TAS or IAS/EAS, but I'm really not sure which, and the difference could be worth 50% in some circumstances.
Anybody know? Bonus points for a document reference anywhere.
G