The extreme heat caused by climate change is posing new challenges to airlines. Air temperature has a powerful effect on the physics of flight, making matters more complicated for aircraft designers and pilots.
On Thursday, a Boeing 787 Dreamliner crashed shortly after takeoff in Ahmedabad in western India. It was more than 100 degrees Fahrenheit, or over 38 Celsius, at the time. So, we asked experts what hot weather means for air safety.
They emphasized that air travel is one of the safest ways to get around, and has been for a long time, even when it’s hot, because pilots are so highly trained and aircraft are built and tested to withstand the worst possible conditions.
That said, heat will probably be increasingly disruptive for airline passengers in the future.
Here’s what you should know.
Getting off the ground
Higher temperatures mean less dense air, and that’s crucial for flight.
Airplanes rely on lift to take off. They speed down the runway until the air rushing over the wing surfaces pushes them up. The less dense the air, the less lift an airplane’s wing will generate and the longer it will take to get off the ground.
Hotter, less dense air can also decrease the amount of thrust that propellers generate, and jet engines might not perform as well because they take in less air.
“The hotter it is, the more airplane performance is degraded,” said John Cox, a former airline pilot and chief executive of Safety Operating Systems, a consulting firm.
Humidity can compound these effects, degrading airplane performance at lower temperatures.
In extreme cases, a runway could simply be too short to accommodate the heaviest planes in the hottest weather. One study found that the hotter the air is, the longer the distance needed for takeoff. That could lead to long delays at airports on very hot days.
But those phenomena are well understood and accounted for in airplane design, and pilots are trained to adjust a plane’s settings to account for different temperatures and altitudes, Mr. Cox said.
“Pilots fly airplanes in a very wide environmental envelope — high altitude, cold, hot — it’s all part of being a professional pilot,” he said.
Blue skies and tailwinds … and turbulence
Climate change is causing the troposphere, the atmospheric layer in which airplanes fly, to warm. This has increased a form of turbulence, called clear-air turbulence, which can be particularly hazardous because it can be hard to spot. And if the planet continues to heat up, turbulence will likely increase.
That’s because a warmer atmosphere can have stronger winds, including in the jet streams where commercial airplanes typically fly. That can give planes a speed boost if they’re flying in the same direction. But it can also cause strong headwinds and more wind shear, which is a sudden change in wind speed or direction.
That can cause turbulence, even if there’s not a cloud in sight.
Airplanes are unlikely to fail because of commonplace turbulence, said Carlos Cesnik, an aerospace engineer at the University of Michigan. But it can be alarming, uncomfortable and, in extremely rare cases, even deadly for passengers who aren’t buckled in. New systems are being designed to improve turbulence detection and to minimize the affects of turbulence, he said.
Planes and pilots can handle the heat
Remember, engineers got humans to the moon and back more than half a century ago.
Modern airplanes are designed to handle the world’s most extreme temperatures and then some. Aviation companies take new planes to the hottest deserts and the coldest deep-freeze zones they can and put them through their paces.
The range of temperatures in that testing process exceeds heat seen at most airports, Dr. Cesnik said. Temperature variability for most commercial flights is small compared with the range of testing temperatures, he added. The companies then plan for heat even in excess of that, creating a large window of weather conditions in which planes can operate.
Extreme heat “is completely accounted for nowadays in plane design,” Dr. Cesnik said. But “not every airplane can operate everywhere, and some airports are more challenging than others.” Airports at high altitude, in hot places or with short runways can pose problems.
The preflight process for pilots includes consulting a model that takes into account local weather, altitude and the plane’s parameters. The model provides pilots with key calculations, like how much runway they need to take off, how to set the wing flaps and what speed to reach. Every time a plane takes off, the pilots get a fresh set of custom calculations.
But human error can still enter the equation.
“Operations ultimately depend on people, and the pilot and the ground crew can get messed up trying to satisfy a bunch of different pressures,” he said.
And because planes can take decades to develop, plane designers should be taking climate projections into account for the next generation of aircraft, said Mary McRae, an engineer at Villanova University.
The bottom line: It’s safe to fly
Flight remains a safe form of travel, even on hot days.
“If the pilots have those calculations, the airplane is safe to fly,” Mr. Cox said. If it’s hot out, the airplane will take longer to lift off. “But am I concerned? Not at all.”
Just keep that seatbelt fastened.
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