Want to know how and where the wheels and brakes of your aircraft get serviced? Read along!
Bringing an aircraft to a safe stop is as important as a perfect take off. Taking good care of the wheels and brakes, therefore, is at the top of the priority list for any airline.
Wheels and brakes encounter tremendous force, environmental and temperature variances on each and every flight.
So how do we know an aircraft wheel needs servicing? Every wheel has a stem of the pin protruding through the cylinder head. This serves as a wear indicator. There is a minimum length of the pin that needs to be protruding for the brakes to be considered airworthy. This limit is ascertained by line maintenance staff, and the entire wheel/tyre assembly or brake is then routed to a workshop for refurbishment.
The wheels of our aircraft have split hubs. It undergoes several rounds of testing before being repaired. The wheels are subjected to nondestructive testing, checking for potentially unsafe cracks, corrosion, wear, and overheating. This includes Eddy current testing and wheel bearing inspections. After the inspection, the wheels are taken to the assembly area.
If the tyres are worn out, they are replaced. Tyres are inflated with dry nitrogen. After the tyres are inflated with required amount of pressure, they are kept overnight for stabilization. The next day, the tyres are rechecked and inspected for any leaks. If there are leaks, they are inflated and kept again for 24 hours. Another round of inspection is carried out after 24 hours. The air pressure inside the tyre should not be less than 5% of the originally inflated pressure.
A Boeing 737-800 has four brake assemblies. The aircraft has a hydraulically-operated multi-wheel piston. There are six pistons and multiple discs with friction pads.
When brakes are applied, hydraulic fluid is applied to all the six pistons uniformly. Hydraulic pressure applied to the piston causes the entire stack of stators and rotors to be compressed. This creates enormous friction and heat and slows the rotation of the wheel.
There are heat-packs that absorb the large amount of heat energy produced when the brakes are applied. Once the pressure is released, that is when the brakes are not applied, the rotors and stators will be free to rotate.