The jet streams on which aircraft surf

On 7^th January, a British Airways Boeing 777 flew from New-York to London in just five hours and 16 minutes, instead of the usual seven hours. An exceptionally short flight time for a subsonic commercial aircraft.

The aircraft’s engines had not been pushed more than usual, but had simply taken advantage of an exceptionally strong tail wind, in this case a jet stream with twice the force than usual. To understand this phenomenon, more pronounced in winter, we went to Météo France, the French national meteorological service.

Alexandre Flouttard,  Weather Forecaster - Aviation Division - Météo France :

"This is the result of a strong temperature contrast in the troposphere, found between the ground, and up to an altitude of ten kilometres (33,000 ft.). The more the contrast between the temperatures are, the more the jet stream speed will be. Gradually, as the altitude increases, the wind speed also increases by up to a maximum of around ten to twelve kilometres (6 to 8 miles)."

During the transatlantic flight, the British Airways Boeing 777 benefitted from a particularly powerful jet stream, with a speed of around 400 km/h (250 mph). The aircraft thus attained a speed approaching 1,200 km/h (745 mph), close to that of the sound barrier.

There was no danger, however, concerning air friction on the fuselage, since the plane was flying with the wind, not against it. Its relative air speed had therefore not changed, it was only its relative ground speed which had increased.

A saving in time and money for an airline. On a New York - London trip, for example, a long-haul can save as much as 15,400 lbs. of fuel thanks to a jet stream, translating into a saving of around 5,000 dollars. In the opposite direction, from east to west, however it is a different story.

Alexandre Flouttard,  Weather Forecaster - Aviation Division - Météo France :

"Since there is the headwind, the speed of the aircraft will be slowed down, not only relative to the ground, but also with respect to the air. So, in general ‘planes avoid the air corridor of this jet stream."

The pilots also have maps of these well known winds, and flight plan calculation software. Tools that allow them to avoid, or alternatively, use these wind currents, in order to ensure maximum flight safety.