Extremely strong winds high above the Atlantic pushed commercial flights close to record-breaking speeds at the weekend, with some passenger planes recording ground speeds of more than 800 miles per hour. Aircraft heading east, including a Virgin Atlantic flight from Washington DC to London, landed considerably earlier than expected due to the freak weather event.
According to tracking site FlightAware, the Virgin Atlantic service, on a Boeing 787 Dreamliner, reached a top ground speed of 802 miles per hour while at 33,000 feet – around 200 mph quicker than average. Rather than taking the usual seven hours, the journey took just six hours and 20 minutes, allowing passengers to disembark 45 minutes earlier than expected.
Did Virgin break the sound barrier?
No. The flight’s top speed was faster than the speed of sound, which at sea level static conditions is 761 mph. The speed of sound, however, varies according to temperature, as well as the medium through which a sound wave is propagating.
As the plane was travelling within 200 mph winds, therefore, its air speed was actually closer to 600 mph, not 800 mph – lower than the speed of sound relative to the environment it was in.
When an aircraft is flying above 25,000 feet, its speed is referenced as a Mach number: a percentage of the speed of sound. An aircraft breaks the sound barrier at Mach 1, creating pressure waves that follow the aircraft. A sonic boom is heard when those waves pass an observer.
Pilots are not, generally, concerned with reaching the speed of sound – which could in some cases prove dangerous. Nick Eades, one of the longest-serving Boeing 747 pilots, notes that commercial planes are not typically engineered to fly that fast.
“In the early days of jet aircraft, there was a phenomenon known as the Mach Tuck,” he says. “As the aircraft reached the speed of sound, the force would make the nose go down, which is a very dangerous situation.
“It has now been designed out of the modern jetliner, but still – you don’t want to get close to the speed of sound because that’s not what those aeroplanes are supposed to do.”
The Virgin flight was not the fastest ever transatlantic civilian crossing – that record is held by BA and Concorde, which flew from New York to London in two hours 52 minutes and 59 seconds in 1996 – hitting a top speed of 1,350 mph. In 2020, another BA flight reached speeds of 825 mph – the fastest ever for a subsonic flight – helped in part by a powerful jetstream. The flight took just four hours and 56 minutes.
The power of the jet stream
While the Virgin flight did not beat this record, it did highlight the power of the jet stream, which pilots use to reduce flight time and fuel consumption. This band of fast-moving winds are found between five and seven miles high in the atmosphere, created by the spread of heat from the equator to the poles. Around 10 miles wide and 2,000 feet deep, westerly winds, in the northern hemisphere, get stronger as the altitude increases.
Manoj Joshi, a professor of climate dynamics at the University of East Anglia, explains: “The jet stream tends to be strongest in winter due to the difference in temperature between the equator and the North Pole. There’s very little variation between time of day, but the jet stream does shift as atmospheric waves and weather systems move along it.”
Thanks to climate change, the jet stream is expected to get stronger in the coming years. Close to the surface of the earth, the polar regions are heating more than the subtropics, weakening winds at lower levels. At higher altitude, however, the reverse is true: the subtropics are warming, and the polar regions are cooler, a quirk of the rotation of the earth.
For passengers, this means that journey times in the Northern Hemisphere are faster when travelling east. “I’ve flown from Boston to London in less than five hours because we had this huge tailwind pushing us along,” says Eades. “But if I was going to fly from London to Boston, it would take me closer to eight hours because I’m flying into that jet stream.”
Pilots use Met Office data to calculate the impact the jet stream might have on a journey, plus the potential reduction in fuel use. A 2021 report from the University of Reading found that flights between London and New York could use 16 per cent less fuel by accurately following jet stream tailwinds. The report also notes that this practice, when performed accurately, is considerably more cost-efficient than other emission-cutting measures.
Jet stream safety
It is unlikely that a passenger would be able to notice the difference in speed until they touch down early. What they might encounter, however, is turbulence as a plane reaches the edge of the weather pattern.
That, according to Eades, is where the danger lies. “As a pilot, you have to be very careful entering and exiting the jet stream,” he says. “It can be a huge difference in temperature and speed.”
That jolt is known as clear air turbulence, which can cause serious disruption in the cabin and is much more difficult to predict than turbulence caused by storm systems or cloud cover. “It’s vital to put the seatbelt signs on and get people strapped in, because sometimes you can know you’re in an area of clear turbulence, but not its exact location,” says Eades.
Regardless of the turbulence risk, the jet stream is still a vital tool in flight route management. As it increases in speed, will airlines utilise it even more often? The answer is complicated. Cathie Wells, a research fellow at The Walker Institute, notes new routing structures, introduced in 2022, are allowing airlines to use the jet stream more readily than in the past. This means that time minimisation is being prioritised – for now.
“Air speed is also a key component of reducing fuel use and emissions,” she says. As the cost of fuel – and the expectation to reduce carbon emissions – increases, planes may lower their speed while flying jet stream-optimised routes. That means transatlantic passengers shouldn’t always expect to arrive home as early as those on the Virgin flight.
By Sophie Dickinson | The Telegraph |
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