Can airliners really reach supersonic speeds?

SUPERSONIC SPEED: A British Airways Boeing 777-200 rode winds of 320km/h across the Atlantic.
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SUPERSONIC SPEED: A British Airways Boeing 777-200 rode winds of 320km/h across the Atlantic.

A British Airways passenger jet reportedly approached supersonic speed this week as it rode a tail wind from New York to London. 

The Boeing 777-200 jet reached a ground speed of 1200kmh as it was pushed along by winds of more than 322kmh across the Atlantic.

At ground level, the speed of sound is 1225kmh.

Passengers arrived an hour and a half before schedule, with a flight time of just five hours and 16 minutes for the journey, according to the tracking website, FlightAware.

There's been recent discussion around widebody airliners flying at near-supersonic speeds by riding a jet stream - the vast river of air that flows west to east at roughly 25-30,000 feet (7.6-9.1km). 

Not since the Aerospatiale-BAC Concorde — capable of cruising at twice the speed of sound — has any commercial airliner been able to sustain supersonic performance, and according to retired Boeing 777 and Airbus captain and current airline flight instructor Lim Khoy Hing, it's not possible. 

In a blog post from 2011, one curious flyer asked whether supersonic speeds had been reached on a flight to London onboard a 777.

Captain Lim explained:

"Even if there is a strong tail wind pushing the plane forward and the ground speed may have exceeded the theoretical speed of sound, in reality, the plane has not gone supersonic.

"The confusion arises between the understanding of ground speed and the plane's speed. The ground speed is the speed at which an object travels relative to a fixed point on the Earth's surface. The difference between ground speed and airspeed is caused by the influence of winds on the overall speed of the aircraft. 

"This is analogous to you walking at 2 kmh along a [moving sidewalk] that is moving at 2 kmh. Your actual movement towards your plane at the gate is pretty fast at 4 kmh (2 + 2) but as far as you are concerned, you are still walking at 2 kmh!"

So there you go. Even if your flight is fortunate enough to have a helpful push from the jet stream, it's not about to go near supersonic speeds in level flight.

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