How Aircraft Can Fly Faster Than The Speed Of Sound Without Going Supersonic

The legendary British-French airliner Concorde took transatlantic operations to the next level with its supersonic capabilities. Air France and British Airways retired this iconic aircraft in 2003, bringing more than 27 years of awe-inspiring supersonic commercial flight to an end. However, did you know that, much more recently, conventional airliners have also exceeded the speed of sound, but without going supersonic?

Aircraft contrails
Did you know that aircraft can fly faster than the speed of sound without technically going ‘supersonic’? Photo: Getty Images

Concorde and sonic booms

As per the Cambridge Dictionary‘s definition, the term’ supersonic‘ refers, at face value, to a vehicle or object moving “faster than the speed of sound.” The speed of sound (at 20 °C/68 °F in dry air) is equal to around 343 meters per second. This adds up to a rapid 1,235 km/h, 767 mph, or 667 knots.

Concorde was capable of cruising at more than twice this speed. It flew 60,000 feet above the North Atlantic Ocean at Mach 2.04, equating to 2,180 km/h / 1,354 mph. When it reached a speed of Mach 1, and passed through the sound barrier, it was known for emitting a so-called ‘sonic boom.’

This loud noise occurs because the pressure waves that it creates inflight become compressed to the extent that they merge into a single shockwave. This then manifests itself audibly as a sonic boom.

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British Airways Concorde Taking Off
Concorde’s sonic boom meant that it was prohibited from flying supersonic over land. Photo: Getty Images

Above the speed of sound but not supersonic

However, when aircraft reach the speed of sound due to atmospheric factors such as wind assistance, they do not experience such a phenomenon. As such, they cannot be said to be flying at a supersonic rate. This is due to the difference between airspeed and ground speed.

For example, to use nice round numbers, an aircraft traveling at 550 mph with a 250mph tailwind would have a ground speed of 800 mph. This would comfortably exceed the speed of sound on the ground, which, as we have established, is 767mph at 20 °C in dry air. However, the aircraft itself would not be moving through the air at 800 mph.

This is because its airspeed, which is measured relatively not to the ground but to the air through which it is traveling, would remain constant at the aforementioned 550 mph. As such, its airspeed remains subsonic, even though, at first glance, its ground speed appears supersonic. Ultimately, an aircraft flies by airspeed rather than ground speed, so the crucial metric is its speed in relation to the air surrounding it.

Virgin Atlantic, Ultra-Long-Haul, Preighters
In 2019, a Virgin Atlantic Boeing 787-9 ‘Dreamliner’ achieved a ground speed of 801 mph in US airspace. Photo: Vincenzo Pace | Simple Flying

Notable recent examples

February 2019 saw a Virgin Atlantic flight from Los Angeles to London land almost an hour early thanks to a sizeable tailwind. At one stage, this atmospheric assistance was so strong that it pushed the aircraft’s ground speed above the speed of sound, to a staggering 801 mph. According to founder Sir Richard Branson, this made it “faster than any other commercial non-supersonic plane in history” at the time.

Last February, a British Airways Boeing 747 set a transatlantic speed record thanks to the strong winds of Storm Ciara. Flight BA112 also exceeded ground speeds of 800 mph, as it raced from New York to London in just four hours and 56 minutes! Its arrival at Heathrow took place an impressive 80 minutes early.

What do you make of this phenomenon? Have you ever been on a flight that has flown faster than normal due to favorable atmospheric conditions? Let us know your thoughts and experiences in the comments.