A Virgin Atlantic flight making the journey from Los Angeles to London yesterday hit a ground speed of at least 1,289km/h, thanks to a streak of fast-moving air in the jet stream over Pennsylvania. You’re probably wondering how, as breaking the sound barrier over land is illegal, but despite surpassing the speed required to break the sound barrier, there was no sonic boom.
And no, the Virgin Atlantic flight wasn’t in some super-special mystery jet that you haven’t heard of. And no, they’re not bringing the Concorde back. Here’s what happened.
The 1,289km/h ground speed of the Boeing 787-9 was reported on the flight tracker system Flight Aware, and was tweeted out by meteorology teacher Stu Ostro:
That #jetstream! ????️ Highest wind speed at 250 millibars in the period of record for those locations near NYC, and for a jet ✈️ over PA last evening an *801* mph ground speed #wow (h/t @gdimeweather, https://t.co/MIqBu7mHNf) pic.twitter.com/RaL2HRQ5Z1
— Stu Ostro (@StuOstro) February 19, 2019
The typical cruising speed for a plane of this size is only around 900km/h, which is a long way off of the speed of sound’s 1,234km/h (although the speed of sound does vary based on altitude, air temperature, pressure, and on and on, and that 1,234km/h figure is based on a reading at sea level under standard conditions).And that’s exactly why there was no sonic boom for this 1,289km/h flight. I’ll let the Washington Post explain:
With a speed max currently over central Pennsylvania, aeroplanes flying through the jet will either be sped up or slowed down big time, depending on their direction of travel. It’s like the moving walkway at the airport. You have your own forward speed, but if you continue this velocity in an environment that is itself moving, it can propel you at an impressive rate.
Commercial aircraft ordinarily can’t break the sound barrier, because they’re not designed to handle the sudden increase in drag and other aerodynamic effects associated with those speeds. Despite a ground speed that high, the plane didn’t come close to reaching that threshold because it was embedded in the swiftly moving air.
So the plane, in this case, was essentially carried along at those speeds by the air around it, so that while it’s ground speed was faster than the speed of sound, its air speed was not. Otherwise the stress of flying near or over the speed of sound would add significant strain on the body of the plane and its control surfaces, and potentially spell disaster. If a plane isn’t meant to go faster than the speed of sound, then it really, really shouldn’t.
Despite not being in the jet stream over the northeast very long, the plane managed to arrive 48 minutes early in London, and most flights headed east over this area of North America are expected to have shorter flight times in the coming days. Of course, any flight going the other direction will either have to fight the wind or go around, so they’re expected to have longer flight times.
The jet streams winds are typically faster-moving in the winter, the Post reports, because of the maximised temperature differences between the northern and southern parts of North America.
It’d be pretty shocking to look at the flight tracker in my headrest infotainment display on a flight like this and see anything north of 1,000km/h, let alone 1,289km/h. The best bonus of the wind boost is that it pushes you past Pennsylvania as fast as possible.