Actually, Airliners Don't Fly Near-Supersonic Speeds

Recently, we’ve seen some discussion of widebody airliners flying at near-supersonic speeds by riding a tail wind courtesy of the jet stream — the vast river of air that flows west to east at roughly 25-30,000 feet.

Flyers have been wowed quick 5-hour and 15 minutes long flights from New York to London and impressive 700 mph-plus speed readings.

On a Boeing 777!

Not since the Aerospatiale-BAC Concorde — capable of cruising at twice the speed of sound — has any commercial airliner be able to sustain supersonic performance. 

But can the average commercial airliner reach supersonic or even near-supersonic speeds? 

According to retired Boeing 777 and Airbus captain and current airline flight instructor Lim Khoy Hing, the answer is no.  

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

The flyer asked if the aircraft’s 760-mph ground speed meant that the plane surpassed Mach 1 — 761 mph at sea level. 

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

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.

Which means you’ll have to join the Chuck Yeager club some other time — and on some other plane!

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