Mac Number on stall-speed
No just for Military bods. Interesting topic for us Civiest Can I pick your brains Mech, too ?
High level, civil transport, asked to hold at high level where hold speeds in the QRH are given both in Mach and IAS. Fellow Captain complied but went very quickly fo manual speed select and wound to speed (rather than Mach) and selected about 210kts rather than the equivelant mach. I , of course gave birth and was reluctant to over-ride a Senior Company (new on type) Commander where I was just a mucky contract guy..
An attempt to advise that Mach gave a flow picture at high altitude and became more significant than IAS fell on deaf ears as round and round we went at high alt at selected 210kts.
Now I was really confused.
Later, bigger transport type, I was offered Max altitude for type in cruise or ,due traffic, descent to much lower alt. Checked the books,graphs and within limits for weight, up we went to 43000ft. Sat there with FMS engaged and although nicely settled on Mach, IAS was terrifyingly low. Couple of minor turbulent bumps left me in no doubt; down we went to the lower level, insufficient fuel at that level to continue and diverted for gas.
I get the theory but practice left me bemused. Tea & bics with CP over the diversion led to to shared confusion over Mac/IAS and he just hunched his shoulders. "Never stop learning-eh?" was his parting shot and I drove home not knowing whether to sit at 70kph or 70mph !