Why the jet stream causes some international flights to arrive early
Passengers on British Airways Flight 112, from Kennedy International Airport in New York to Heathrow Airport outside London, received good news early Thursday morning. The flight, which would normally have taken about six hours, was due to arrive 50 minutes early.
Other flights traveling east across the Atlantic this week are arriving ahead of schedule, in some cases up to an hour early, thanks to a jet stream blowing in their favor.
For example, a United flight that departed Tuesday evening from Newark Liberty International Airport arrived at Charles de Gaulle Airport near Paris 58 minutes early, a flight that normally takes about seven hours, according to the report. Flight consciousa site that tracks airline traffic.
An Emirates flight on Tuesday from Dallas Fort Worth International Airport to Dubai in the United Arab Emirates was expected to take 13 hours and 44 minutes. According to FlightAware, the plane landed 57 minutes early.
Here’s what you need to know about these early arrivals.
What is a jet stream?
A jet stream is a band of strong winds that blow from west to east in the upper atmosphere, or about 30,000 feet above the ground, according to the National Oceanic and Atmospheric Administration.
One way to understand how a jet stream can affect flights is to think about a boat on the water, said Jennifer Stroozas, a meteorologist at the National Weather Service’s Aviation Weather Center.
“The atmosphere behaves a lot like a liquid,” she said. “When the water is calm, a boat also remains still. If the water has a strong current, it will naturally push a boat.”
When planes fly within a jet stream, strong winds can propel the plane faster, Ms. Stroozas said.
Commercial flights typically fly at a speed equivalent to a ground speed of about 570 miles per hour, according to Richard Levy, an aviation consultant who used to fly commercial planes.
The jet stream over the Atlantic Ocean has caused flights to travel faster than their average speed this week. For example, the British Airways flight from New York to London reached a flight speed of 1,200 km/h
Jetstream flights are not rare.
Kevin Kuhlmann, a professor of aerospace sciences at Metropolitan State University of Denver, said it was common for jet streams to accelerate flights from west to east.
In summer it is more common for flights to be affected by a jet stream when they are further north. In winter, the jet stream can shift south, Mr. Kuhlmann said.
That shift “could create a situation where traffic gets a boost,” he said.
Jetstream-supported flights are not limited to flights crossing the Atlantic Ocean. Mr. Levy said he was used to jet streams speeding things up as he flew east over the Pacific Ocean.
Jet streams can also increase the speed of domestic flights. A jet stream that swept across the United States in February 2019 aided flights to the east arrive well ahead of schedule.
Turbulence can be a problem.
Air currents aren’t always a boon for pilots and travelers, experts say. Flying through a jet stream can cause turbulence problems in some cases.
To avoid problems with turbulence, Mr. Levy said, pilots will sometimes travel at a slower speed. He said flying through a jet stream can be like driving on a bumpy road.
The faster someone drives on a bumpy road, “the worse it is for the car and for you,” Mr. Levy said, adding that it is better to drive more slowly in such situations.
“That’s exactly what we do with turbulence,” he said. “We’ll bring it back.”
Pilots most often experience turbulence when traveling in and out of the jet stream, Mr. Kuhlmann said.
“That transition area will certainly bring the possibility of turbulence,” Mr. Kuhlmann said. “But just because you’re in it doesn’t mean it’s dangerous.”
Still, turbulence can be a problem on any flight, whether jet stream or no jet stream, Mr. Levy said. Pilots remind passengers to fasten their seat belts so they can be safe, and they keep in touch with air traffic controllers who can warn them of the possibility of turbulence.
Flying back may not be that quick.
Planes traveling from west to east may be aided by strong easterly winds, but the same currents can have the opposite effect on a plane heading west.
“The opposite is also true,” Ms. Stroozas said. “If it were flying into a strong wind, it would effectively slow down, much like trying to paddle upstream.”
It is possible to avoid flying west in a jet stream, Mr. Levy said, because, “A, it slows you down; B, you’re going to burn gas like crazy with nothing in sight; and C, the turbulence.” Sometimes it can’t be avoided given the route of a flight, he said.
On a westbound flight from London to New York City, Mr. Levy said, the jet stream can be largely avoided by flying north over Greenland.
“We don’t go anywhere near it,” he said.
An early arrival is not always best.
Arriving at a destination early is usually good news.
“I’d like to get to Chicago’s O’Hare early,” Mr. Kuhlmann said.
He added: “But guess what? There is no gate for you” if you land the plane too early.
The potential problem: Passengers could sit on the plane, stuck on the ground, while the crew waits at a gate so everyone can get off.
Mr Levy said waiting for a gate is a less common annoyance for travelers at some airports in Europe, where gates are dedicated to certain airlines. Flight tracking computers also help prevent delays on the ground.
“Once the wheels are off the ground,” he said, “the computer immediately knows what your flight time is.”