How high temperatures affect takeoff

Denver International Airport’s (DEN) Runway 16R/34L stretches 16,000 feet -- just over three miles, making it the longest commercial runway in North America.

Of DEN’s six runways, five are 12,000 feet long. You might wonder why Runway 16R/34L is 4,000 feet longer. The answer is that high-elevation conditions require additional runway length to help accommodate departures during hot summer conditions.

At high elevations, the air is less dense. Summer heat makes it even less dense, leaving fewer air molecules in a given volume. This means the wings need a higher true airspeed to generate the lift needed for takeoff, while the engines can produce less thrust. The result is a longer takeoff roll before the aircraft becomes airborne.

The runway does not literally become shorter. The aircraft simply needs to use more of it, leaving less distance in reserve. (Here's an interesting tidbit about pavement temperatures: In direct summer sunlight, dark asphalt can reach surface temperatures around 150°F, well above the surrounding air temperature.)