threemiles;
Pointless numbers unless you know what the actual ISA deviation was. Can be very very significant in a tropical storm, maybe ISA+40 and then?
Well, for a given SAT rise and a maintained Mach and CAS, only the TAS increases. ISA+40 would yield about a 39kt TAS increase but the Mach remains at M0.82, the CAS at 279kts.
ISA+40 is pretty rare and it would seem you're not likely going to be staying at 350 at ISA+40. The Environmental Limitations (ATA90) doesn't list a maximum TAT but the graph shows 350 and a SAT of -20 as right on the FL350 line. The AOM doesn't have cruise performance charts for anything other than ISA and the Optimum weight for 4000ft step climb has ISA+10 and ISA+20. ISA+20 @ M0.82 shows a climb from 310 to 350 at an optimum weight of 226k kg's however. So ISA+40 may not present the serious issues we might have first thought. You were thinking of a column of much warmer air, as per the earlier conversation in re Tim Vasquez' work could possible stall the aircraft? Otherwise, not sure what you're thinking.
Your notion brings to mind an accident that occurred on the Vancouver coast - Fraser river delta, when a heavily-laden fishboat sank, costing five lives, if I recall. The ship was in salt water and when it entered the less bouyant fresh water of the Fraser's outpouring, it became unstable.