Definition
The structural shafts that pass through the center of an airplane's wheels and around which the wheels rotate. Axles transfer the airplane's weight from the landing gear struts to the wheels and tires, and they hold the wheel bearings that allow the wheels to turn freely during taxi, takeoff, and landing.
Plain English
The metal rods that go through the middle of the wheels and let them spin. They carry the weight of the airplane down through the landing gear into the tires.
Context Anchor
Seen in landing gear, tire, and brake discussions, especially when identifying the parts that carry wheel loads during taxi, takeoff, and landing.
Derivation
From Old Norse 'oxull' meaning a shaft or pole. The word has meant 'the rod a wheel turns on' for centuries, in carts, cars, and now airplanes. The aviation meaning is the same as the everyday one — there is no special twist.
Why Pilots Care
Axles are checked during preflight as part of the wheel and brake assembly. A damaged axle, loose nut, or failing wheel bearing can cause a wheel to seize or come off during landing, so pilots and mechanics inspect this area for signs of wear, leaking grease, or heat damage.
Analogy
On a small cart, the wheels turn around a metal rod. On an airplane, the axle serves the same basic purpose, but it must handle much higher loads.
Intuition Check
Do not think of the axle as the whole landing gear leg. The axle is the part at the wheel that supports the wheel and lets it rotate.
Example Sentence 1
During preflight, the pilot checked the axles and wheel assemblies for any signs of damage or grease leakage.
Example Sentence 2
Proper lubrication keeps the wheels turning smoothly on their axles.