newswatcher
INS/IRS read-outs on the flight deck are generally displayed in knots, and personally speaking, I wouldn’t place too much reliance on the accuracy of the mph/kph conversions displayed on the cabin IFE screens.
Concorde cruise-climbs at M2.0, so at typical altitudes of say around FL580, and assuming ISA temperatures, this would broadly equate to a ground speed of 1,150 kts (1,320 mph) in still air.
At these altitudes, the winds tend to be light - as the strong jet streams that subsonic aircraft sometimes experience tend to die off above about FL450 - so we don’t often see indicated ground speeds above 1,200 kts (1,380 mph).
I’ve seen a ground speed of 1,218 kts (1,400 mph) a few times, but never, as yet, 1,260 kts (1,450 mph).
We suspect that the TU 144, which was originally aiming for M2.35 (1,550 mph), actually cruised nearer to M2.05, which would have given it a ground speed of roughly 1,350 mph in still air, probably still fast enough, just, to take the title of fastest commercial? aircraft.