You may have seen the stories – the jet stream over the Atlantic has been unusually strong during the last couple of days. The 777 in question had reached speeds of up to 745 mph.
I flew from Tokyo Haneda to San Francisco on a JAL 777 yesterday and was a bit surprised when reading the flight parameters.
Holy smokes – 802mph! With a tailwind of up to 245 mph! Parts of the flight were very turbulent (no big bumps, but steady up and down in a violent fashion). Many airplanes fly at only 245mph and the pilot directed us into 245mph tailwind zone!
Supersonic speed starts at 768 mph, so did the 802mph shown in the plane's flight tracking system mean that it went supersonic?
Of course not, since modern jets are not made for supersonic flight and the top cruising speed is just 590mph for a 777.
The explanation is simple: the plane traveled 802mph relative to a point on the ground but 'just' ~550mph relative to the surrounding air – which is usually called airspeed and the speed relevant to supersonic flight.
Of course I arrived one hour early (well-shaken not stirred) into San Francisco. A 777 consumes about 2,100 gallons per hour at cruising speed, so at about the current $1.51 per gallon, that is $3,000 saved.