Why are commercial aircraft tires filled with nitrogen?

- Feb 21, 2020-

In 1986 a Mexicana Boeing 727 crashed, killing 166 people. One of the contributing causes of the crash was the explosion of a main landing gear tire inside the wheel well which ruptured some fuel lines, causing an in-flight fire.

A dragging brake caused the tire to overheat, producing flammable vapors inside it. The vapor combined with the internal pressurized air, and the temperature reached the autoignition point causing it to explode.

In 1987 the US FAA released airworthiness directive 87–08–09, applicable to most large aircraft in service at the time:

  • To eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile gases from the tire inner liner producing a tire explosion, accomplish the following, unless already accomplished:

    • A. Within 180 days after the effective date of this AD, to ensure that all aircraft tires mounted on braked wheels do not contain more than 5 percent oxygen . . .

After the AD, the regulations were changed so that:

  • (e) For an airplane with a maximum certificated takeoff weight of more than 75,000 pounds, tires mounted on braked wheels must be inflated with dry nitrogen or other gases shown to be inert so that the gas mixture in the tire does not contain oxygen in excess of 5 percent by volume, unless it can be shown that the tire liner material will not produce a volatile gas when heated or that means are provided to prevent tire temperatures from reaching unsafe levels.

Even at that time it was more practical to use high-pressure nitrogen (with a very good regulator) to service tires, since most common air compressors don’t reach high enough pressures for heavy aircraft tires, but apparently Mexicana had some means of using air.