Originally posted by RobG: So the true airspeed was even higher than the rated maximum speed?
What was your source for the speed? If a typical passenger info display it would either be TAS or Ground Speed (GS). Highly unlikely the acft would be intentionally operated outside of its operating limits. I suspect the speed you saw was TAS.
One plans, flys and navigates by
True airspeed, but what the acft 'sees' is the indicated speed (IAS) sensed via the impact pressure in the pitot system. As you go up the air density decreases so the airspeed shown on the airspeed indicator is lower than the true speed through the air (TAS). Calculations based on altitude and temperature translate IAS into TAS.
Above a transition altitude jets set speed as a percentage of the speed of sound (which also varies with density altitude) and also provides a direct means of avoiding Mach boundary performance issues. Mach buffet may be anything from a slight nibble to a nasty bite. Mach-plus jets slip through that zone with no buffet but normally experience a pitch trim change as the shock wave boundary moves.
The DC-8 is the only non-Mach airliner I know of ever certified at Mach-plus as it accidentally crept up to M 1.01 in a dive during certification testing at FL 410. You could point the A-6 Intruder straight down even with clean wings however, and it just bogged into its own bow wave at about M 0.9.
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