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Too hot to fly

This is a nerd post!

The Washington Post has an interesting story today about how flights in and out of Phoenix have been canceled this week because of the heat: It’s so hot in Phoenix that airplanes can’t fly

The story is misleading in that it suggests that particular models of aircraft have maximum operating temperatures. But it’s more complicated than that. Though no doubt there is a maximum operating temperature, there also is a maximum takeoff and landing temperature, which might be much lower.

The efficiency of an airplane, and thus its ability to take off or land on a given runway, actually is a formula with a number of factors. The factors include the weight of the plane, the air temperature, the altitude of the airport, and even the humidity.

Hot air is thinner than cold air. Air at high altitudes is thinner than air at low altitudes. Thinner air affects not only the airplane’s airfoil (its wings); thin air also affects the efficiency of the airplane’s engines. So, to determine whether an airplane can fly in a given situation, a flight computer must make a calculation on all these factors — plus, of course, the runway length and the altitude of any high terrain around the airport that must be cleared.

As a student pilot many years ago, it was easy to feel, just from the controls of an airplane, that airplanes are perky and responsive on cold days, but also that they’re sluggish and much more disobedient on warm, humid days, or at mountain airports.

But the thing that really brought this point home to me was flying on a packed-to-the-gills Air India flight from Bangkok to Delhi some years ago. Those heavily loaded flights into and out of New Delhi, I learned, usually land and take off in the middle of the night. Why is that? Because it’s too hot for the planes to fly during the daytime. And in my limited experience, Air India planes are packed to the max, so air temperature becomes a critical factor.

I wouldn’t worry, though. Today’s airplanes are incredibly sophisicated, and their behavior is easily modeled. If your flight to Phoenix is canceled, it’s because the airlines know their business and their airplanes. Still, unless it’s hotter than the airplane’s maximum operating temperature (which I doubt), the plane would be able to fly with a lighter load, even in the heat. But these days, airplanes tend to be packed, and apparently it makes more business sense to cancel a packed flight than to drag enough people and their luggage off the plane to lighten the plane enough to satisfy the OK-to-fly computation.

One Comment

  1. Jo wrote:

    Interesting post. Have only been to Phoenix a couple of times and once was in August. Very hot! So much development has added roads,etc., and concrete and other paving materials do tend to retain heat in hot climates.

    Wednesday, June 21, 2017 at 5:31 pm | Permalink

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