Science

No, airplanes weren’t breaking the sound barrier this week

Bob CollinsBob Collins Feb 20, 2019
18

The person I picked up while Lyfting last night at the airport was exhausted. “It was like flying to Los Angeles,” he said of the more than three-hour flight from Boston.

He was the victim of nature to an extent rarely seen, and he’s the yang to the yin of the focus of stories about what’s happening up there.

Wind. Really fast wind.

Also: really questionable understanding of science and dynamics.

“The jet stream is moving so fast right now that commercial planes are traveling faster than the speed of sound,” The Week blared in its headline.

“Jet stream helps flight reach 801 mph,” said Fox News said, pointing out that the speed of sound is 776 miles per hour.

The Los Angeles to London flight “topped out at 801 miles per hour, technically meaning it was traveling faster than the speed of sound,” the Boston Globe’s reporter writes.

OK, let’s get technical. That’s preposterous.

“It only broke the sound barrier in terms of ground speed, mind you,” Popular Mechanics says.

That’s not how breaking the sound barrier works either.

First, the speed of sound is not a fixed number. It’s a calculation that considers temperature and density of the mass through which the object is traveling.

As for how fast the jets were traveling yesterday, the airspeed indicator on the flights — both eastbound and westbound — were the same in both directions; pretty much the same as they always are.

Since the airplanes are always in a moving mass, even if they were theoretically stationary in the mass — just hanging there with no power — they would still have been moving across the ground at about 200 mph — either forward or backward — but the airspeed would be be zero.

It’s astonishing, for sure, that the tailwinds and headwinds were that strong, but the sound barrier was never threatened. And — as long as we’re talking about Mach I technically — it’s impossible for a commercial jetliner to break it.