The Science Of Why It's Too Hot For Some Planes To Fly In The Southwest U.S.

Interesting. I anticipated that it would be due to hot air being less dense, which was accurate, but I was thinking only about the amount of force generated by the engines, so that less force would be generated for the same amount of engine speed. That is a factor, but another is the effect on the lift capability of the wings:

https://www.forbes.com/sites/marshallshepherd/2017/06/20/the-science-of-why-its-too-hot-for-some-planes-to-fly-in-the-southwest-u-s/#77ea88e754ce

Marshall Shepherd
June 20, 2017

The National Weather Service in Phoenix, Arizona confirmed on Tuesday morning that a record high temperature was set Monday June 19th. The temperature was 118 degrees F. This tied the record set only a year ago in 2016. The National Weather Service also tweeted this ominous statement

......If we hit our forecast highs Tuesday and Wednesday it would set 2 new records. #azheat

Across the southwest United States, heat experienced "less than once per year on average" is happening, and it is dangerous. Ironically, a new paper released Monday in the peer-review journal Nature Climate Change found that extreme heat like that being observed in the Southwest U.S. and in Portugal will become more common and intense. The study also finds that the number of people globally affected by 20 days or more of intense heatwaves (dangerous temperature and humidity) will jump from 1 in 4 currently to 3 out of 4 by 2100.

This is consistent with a 2016 National Academy of Science report that concluded that contemporary heatwaves are increasingly linked to climate change. Such heat is obviously a human health concern, but there is another disruption that you may not think about. Extreme heat affects air travel. Believe it or not, it is unsafe to operate many of the airplanes currently in use by major airlines when temperatures are this hot, and science explains why.

The Arizona Republic reported that around 50 flights for Tuesday were cancelled at Phoenix Sky Harbor International Airport. These were primarily regional flights. According to The Arizona Republic

a statement from American Airlines, the American Eagle regional flights use the Bombardier CRJ aircraft, which has a maximum operating temperature of 118 degrees. Tuesday's forecast for Phoenix includes a high of 120 degrees, and the flights that are affected were to take off between 3 and 6 p.m.....Larger jets that fly out of Sky Harbor have higher maximum operating temperatures: Boeing, 126 degrees, and Airbus, 127 degrees

The science behind why airlines struggle in extreme heat is rather simple. Patrick Smith is a pilot and author of the book Cockpit Confidential. In 2013, Business Insider considered the question of why aircraft struggle in extreme heat. While heat is stressful on some of the planes internal parts, physics is the main reason. Business Insider quotes Smith's writing:

Hot air is less dense. This affects the output of the engines as well as aerodynamic capabilities, increasing the required runway distance and reducing climb performance. Therefore the amount of passengers and cargo a plane can carry are often restricted when temps are very high......How much so depends on the temperature, airport elevation and the length of the available runways. And getting off the ground is only part of it: once airborne, planes have to meet specific, engine-out climb criterion, so nearby obstructions like hills and towers are another complication.

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An airplane's wing is designed in such a way (see below) that lower pressure is created as air flows over the the top of the wing, and higher pressure is found beneath the wing. The difference in pressure (gradient) creates lift. If there is not sufficient airflow to create the pressure difference, there is insufficient lift. Extreme heat conditions, as noted above, make it difficult to generate the required lift for planes to take off or land.

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For me, this is one of many ways that extreme heat (and likely climate change) affects your life and our economy that you may not realize. This is not about polar bears or penguins. It is about our day-to-day commerce, economy, and convenience.