I have always understood that "coffin corner" is when the TAS for the stall
increases to meet the onset of compressibility or whatever which occurs at
Mach 1. I understand that the TAS of Mach 1 does not change with the
reduced density at altitude, whereas of course the TAS of the stall
increases.

I am sure I remember reading years ago that "coffin corner" was the
limitation for the maximum altitude for operating the Boeing B47.

W.J. (Bill) Dean (U.K.).
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"Jim" wrote in message
...

Still thinking about VNE and whether it is usually stated as a TAS
rather than an IAS (one must read the POH to be sure, of course).

I've gotten the notion, probably from comments I've not understood
very well, that the "coffin corner" is the intersection of stall speed
as an IAS indication on the airspeed indicator, and VNE understood as
a TAS and thus occurs at a decreasing IAS with altitude.

I guess the consequence of this notion is that as aircraft altitude
goes up the stall speed TAS goes up to ultimately bump into
the VNE TAS. If VNE is published as an IAS, like stall speed,
then stall speed and VNE would never converge.

Or maybe it was the Manoeuvring TAS that could bump into the VNE TAS.

Is this what is sometimes referred to as the "coffin corner"?