Heat Waves Make for Less Friendly Skies

Recently, a United Airlines flight to Phoenix was forced to turn around and head back to Houston. The reason for the diversion? Extreme heat. With global temperatures rising, is this a sign of things to come?

The answer is both yes and no.

Marilyn Smith, a professor and associate director at Georgia Tech’s Vertical Lift Center of Excellence in Atlanta, says the aerospace industry has been addressing this problem for the past decade.

“We are designing new engines that are a lot more efficient and new aircraft designs. We’re not going to see the same old tube and wing designs of today,” Smith says.

Smith says aerospace engineers have been looking for ways to decrease the need for more runway length not because of temperatures, but because of noise restrictions. Either way, newer designs and more efficient engines will help the airlines address increasing heat issues.

Planes flying in extreme heat need either a longer runway or less weight for takeoff and landing because of the laws of aerodynamics.

“As the temperature increases, the density of the air on the runway decreases, which decreases the lift force on the wings of the plane. That, of course, makes it more difficult for it to take off,” explains Paul Williams, a Royal Society University research fellow in the department of meteorology at the University of Reading in the UK.

Weight restriction days — that is, days when planes can’t take off without removing either passengers or cargo — have increased fourfold since 1980, Williams says. “It doesn’t happen very often, but the projection is that we’ll see an increase in the number of weight restriction days by between 50 and 200 percent in the coming decades, as the globe continues to warm,” Williams adds.

Pilots must also be aware of their rate of climb, especially at airports surrounded by mountains, says Marilyn Smith. “You’re not going to climb as fast on a hot day and so you have to be careful. You don’t want to hit those mountains.”

Right now, most large commercial planes are designed to function at operational standards up to about 126 degrees. Smaller regional jets max out at about 118 degrees. That’s why the plane heading for Phoenix turned back when thermometers started reading 120.

Rising global temperatures may affect air travel in other ways, too. The prevailing winds on transatlantic routes are expected to be significantly stronger by the end of the century — perhaps 15 percent stronger, says Paul Williams. This means stronger tailwinds for eastbound flights and stronger headwinds for westbound flights.

“We’ve calculated that this is going to double the likelihood of a transatlantic plane crossing the Atlantic in less than five hours and twenty minutes,” Williams explains. “We’ve [also] calculated that it’s going to double the likelihood of a westbound flight across the Atlantic taking more than seven hours — and it’s possible that these changes are already happening.”

In fact, he says, one eastbound flight from New York to London took only five hours and sixteen minutes, which broke the record for the fastest non-Concord crossing; and two westbound flights from London to New York took so long the planes had to stop in Maine to refuel.

Yet another consequence of a stronger jet stream is more turbulence. Williams has calculated that incidents of clear air turbulence on transatlantic flights could double by the middle of this century.

“I’ve seen statistics showing that the number of accidents caused by turbulence has grown by a factor of five since 1980,” he says. “That’s three times faster than the growth in air traffic. Now, it’s too early at this stage to blame that on climate change, but the science is clearly telling us to expect a long-term upward trend in turbulence in the coming decades.”

Finally, we may need to be concerned about the airports themselves. During Hurricane Sandy, both New York JFK airport and LaGuardia were under water. San Francisco International airport is only 4 meters above sea level. Amsterdam Airport Schiphol is actually three meters below sea level.

“It could be that low-lying coastal airports could be threatened in the future by a combination of sea level rise, storms and tides,” Williams predicts.

– Adam Wernick (originally published at PRI.org)