Nitrogen is used primarily to prevent oxygen permeation through tyres and for undercarriage strut pressurisation.

During take-off , landing and at altitude, aircraft tyres undergo a wide range of temperatures and pressures. If filled with compressed air, the oxygen content tends to permeate through the tyre wall and cause tyre deflation. Filling with compressed nitrogen prevents this from happening, ensuring aircraft land safely on correctly inflated tyres.

The landing gear struts in simple terms, are comprised of compressed gas, and oil, acting as a shock absorbing damper and spring. Nitrogen is used as the compressed gas because it is less likely to permeate through seals causing loss in pressure, and being inert, is a safer alternative to air due to the heat generated by sudden compression on landing.