Here we are, about 24-hours away from the beginning of the summer solstice and most of the desert southwest is broiling. For the record, I thought Summer 2017 began in these United States on Wednesday, June 21st. As it turns out, it does for those living in the Eastern Daylight Time (EDT) zone. According to the Famers Almanac, Summer 2017 will arrive at 12:24 a.m. EDT. For those of us in the Central (CDT), Mountain (MDT), and Pacific (PDT) zones, summer will arrive on Tuesday, June 20, 2017, at 11:24, 10:24, and 9:24 p.m., respectively.
The heat advisories began last week, with projections of high temperatures between 119 and 121 degrees Fahrenheit (F) on this Tuesday and Wednesday, June 20 and 21, 2017. As seasoned Phoenicians know, it gets hot here in the summer, and we attempt to make the best of these torrid conditions. While 119 and 121 degrees F seem off the charts for my relatives and friends east of the Mississippi, these numbers are not new to us nor do we see them every summer. When we do, we hope for just one or two days under the sweltering conditions that accompany them.
Local meteorologists have been discussing the extreme heat that we are experiencing across most of Arizona and the desert southwest, and they also advised of the possibility of airport delays and/or closures. Most of us are familiar with weather conditions that can ground airplanes and leave one stranded at the terminals. These include fog, wind, snow, and thunderstorms. However, extreme heat is usually not on this list. That led me to ask why is that?
This is not the first time I have asked the why? question! Back in 1987 or 1988, I was delayed departing Sky Harbor Airport due to excessive heat conditions. When I asked “why?” back then, I was told by one of my fellow passengers that the tires on the landing gear had not been tested above a certain temperature, say 115 or 116 degrees F, and the pilots couldn’t be certain if the tires would explode while attempting a landing on the tarmac. At the time it sounded like a good answer, however, it turns out to be an urban legend.
According to Pilot Friend, the figures published in the Flight Manual for the performance capabilities of a certain model of airplane are always related to standard atmosphere (29.92 inches of mercury at 15 degree Celsius (C) [59 degree F] at sea level). However, only rarely will the airplane actually operate under conditions that approximate standard atmosphere. Any increase in temperature or altitude means a decrease in the aircraft’s optimum performance. [Ref 1]
Weighing in on a similar question from Business Insider, Patrick Smith, and airline pilot, blogger and author of Cockpit Confidential provides this answer [Ref 2]:
Serious heat can damage a plane’s internal components, which is why some aircraft have maximum operating temperatures. But the heat also makes it harder for the plane to get off the ground at all.
Smith goes on to say:
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.
Another concern that is often overlooked are the airline employees working on the ground. Temperatures on the tarmac can rise 15 to 20 degrees above ambient levels. Heat comes off of the concrete and the equipment making the servicing of incoming and departing planes even more difficult.
Staff at Sky Harbor airport add that while most of the larger planes like Boeing and Airbus models that fly in and out of Phoenix can handle higher ambient temperatures between 126 and 127 F, some of the smaller commuter planes cannot.
American Airlines recently announced some of their regional planes have a limit of around 118 degrees, so some flights may be cancelled between 3 and 6 p.m. Monday through Wednesday of this week or longer if the extreme heat conditions persist.
- Effect of temperature and altitude on airplane performance, Pilot Friend, http://www.pilotfriend.com/training/flight_training/aft_perf.htm
- Why Planes Can’t Fly in Extreme Heat, by Alex Davies for Business Insider, July 1, 2013, http://www.businessinsider.com/why-planes-cant-fly-in-extreme-heat-2013-7