In a modern Airliner you can't get near "coffin corner" without busting MMO so we should coin a new term for the limiting alt where MMO and AoA stall coincide.
No, normally it is reached at a much lower Mach than Mmo.
Actually, the term "coffin corner" refers to a very small window between mach buffet and stall, not loss of control.
That is the accepted concept nowadays, in the FMS era.
Airfoil you can reduce power and use attitude to maintain airspeed. Airspeed is the critical factor.
Very much so and anyone who's used a HUD can testify to that principle.
Coffin corner in fact is a sensationalist description of approaching the *
maximum reachable ceiling* at a given aircraft weight.
The Turcat formula shows that there is a point at which Cl max will be reached and will prevent a further climb
whatever the available thrust as one would hit at the same time high and low stall.
It is to be remarked that this ceiling would be attained at only one Mach number.
Now, an airliner is normally operated at altitudes where there is a g factor protection ( as g increases the "apparent" weight ) and one would find those graphs in any QRH. Those protected graphs also exist ,in an easily exploitable form, in the FMS computations of MAX ALT.
So, in real airliner pilot's life, one would be flying with a reduced spread of Mach numbers and that spread will increase at the same altitude as we burn fuel and the airplane gets lighter and lighter. For instrance on a 60T A-320, that altitude (Mach and stall buffet) is 39,000 ft / Mach .78.
At 37,000 ft,flight is possible between .73 and .82 Mach (Mmo)
At 35,000 ft, it is between .70 and .82 Mach.....etc... etc....
From this, the inference is that the best *escape* will be to slowly reduce power (it's almost infinitesimal in the beginning) and start losing altitude at the Mach number one was at. And, yes, maintain Mach with the pitch control (what we do ususally in FL CH or OPEN DES, btw), and very soon, the margins will increase on both "sides" of that Mach.