The Boeing 777X landing gear is displayed during the Farnborough International Airshow 2022 on July 18, 2022 in Farnborough, England. John Keeble/Getty Images
FlightAware (the world's most extensive real-time flight tracking and data platform) follows thousands of airborne aircraft. Typically, there are between 12,000 and 14,000 planes in the sky at any given moment, with approximately two-thirds of those consisting of commercial flights.
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Depending on the plane's make, model, and size, each can have as many as 22 tires (for the Airbus A380). Boeing 717s, 727s, and 737s (some of the most active and common commercial aircraft) all have six tires, while a 747 has eighteen. The Antonov An-225, the world's largest plane before it was destroyed in 2022 during Russia's invasion of Ukraine, had 32 total tires. As a frame of reference, the main tires on aBoeing 777 are over four feet across and weigh 265 pounds each, while the nose wheels are smaller at 43 inches x 17.5 inches and weigh about 155 pounds. That's a lot of huge and heavy tires in the sky simultaneously.
Unlike the tires on an automobile filled with compressed air, those on a commercial airplane are filled with inert nitrogen, which has been the case since the late 1980s, when the U.S. Federal Aviation Administration (FAA) first made the mandate. There are actually several reasons why inert nitrogen gas is used. The primary one, however, is because it's non-flammable and won't combust if one of those tires decides to burst during the relatively brief periods they're landing or taking off and encountering their most extreme temperature and pressure variations.
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Nitrogen's lack of interaction is the key
A passenger plane taking off airport with tire tracks from previou airplane tires left marks on the runway. muratart/Shutterstock
On average, commercial planes are going anywhere between 160 and 180 mph when they take off and 130 and 160 mph when they land. Since oxygen is a highly flammable gas that will in and of itself explode simply by being exposed to a heat source, it was considered a good idea to start filling them with an inert gas that wouldn't create a massive explosion. Nose wheel tires (which are used more because they steer the plane as it taxis to and from the terminal) have a lifespan of between 200 and 350 landings, while the rear main-wheel tires average between 300 and 450.
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The pressure in oxygen-filled tires changes based on the altitude, and can expand and contract with temperature variations. Since planes have a cruising altitude between 31,000 and 42,000 feet (5.9 to 7.2 miles), the tires would have to adjust to vastly different altitudes and incredibly contrasting temperatures consistently. While it can be nearly 120 degrees Fahrenheit at the Harry Reid International Airport in Las Vegas, Nevada, at typical cruising altitudes, say, of 36,000 feet, the air temperature is around −65°F. However, because nitrogen is an inert gas, it is immune to such things and can maintain stable pressure.
Finally, nitrogen is naturally dry, holds no moisture, and doesn't turn into solid form until it hits -279.4 F. Compressed air doesn't "freeze" per se, but the moisture in it can at a mere 32°F. Moisture causes corrosion, which in turn promotes rust, thus nitrogen's dryness increases both the safety and longevity of the tires.
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