It goes without saying that aircraft maintenance is crucial not only for the efficient performance of modern commercial and jet liners, but most importantly – safety of flight. Airbus just published a case study with recommendations to all operators that overlooking proper care of wheel bearings can have disastrous consequences.

Airbus emphasizes that improper maintenance can lead to severe part failures, including fire and the loss of an entire wheel and tire assembly during takeoff or landing. The event that inspired the maker’s notice to operators was an aborted takeoff in Brussels that left debris strewn all across the airfield.

Friendly Advice From Airbus

Credit: Airbus

Airbus extensively analyzed the root causes of an incident in which one A330 suffered the catastrophic failure of a landing gear wheel during takeoff. The analysis showed that the wheel bearing failed, which caused it to lose its location and violently self-destruct, damaging brakes and hydraulic lines before being completely ejected from the main landing gear.

Airbus says that the full investigation has not been completed, but signs indicate that improper maintenance was the most likely culprit in this case. Each wheel in the Airbus A330 landing gear has two taper roller bearings inside it. These bearings are crucial to keeping the wheel position correctly in the assembly as well as transferring the load of the aircraft between the gear assembly and the ground.

Airbus does not name the incident in its case study, but a comparison of photos and event descriptions on the Aviation Herald reveals a perfect match for a 2017 mishap. The interim report by the Belgian AIB describes the aftermath in these words:

“A separated half of a half wheel rim was still present. The hydraulic lines were cut, and fluid was leaking…The tyre was found nearly intact in the grass located right side of runway 01 north of F2.”

The Incident In Question

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The maintenance bulletin stems from a mishap that happened all the way back in 2017. An Air Canada (AC) A330-300 with 179 passengers aboard began its takeoff roll at Brussels Airport (BRU) on February 5th. The crew rejected the takeoff when its right main gear lost multiple tires. The jet was already up to high speed as it attempted to depart for Montreal International (YUL), but instead came to rest on a taxiway.

Airbus says that an A330 taxied to its departure runway, and the flight crew had to use more engine thrust than normal to position the plane. The pilots did not suspect a mechanical fault as the runway had an uphill incline. The case study says that when the plane reached a speed of 70 knots, a loud bang erupted and brake alerts blared in the cockpit.

The aircrew immediately aborted with the plane’s speed maxing out around 80 to 90 knots on the tarmac. As the aircrew slowed the widebody down for an emergency stop, the brakes were weak, and only one reverse thruster responded to controls. Emergency crews met the stricken jetliner on the runway and found a wheel completely missing from the front, right-hand main gear. The parts and pieces of it had scattered all over the runway after it exploded.

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Maintenance’s Crucial Role In Safety

Credit: Airbus

The wheel bearings inside the landing gear are machined precisely for low friction to minimize the wear and tear, as well as the heat generated during ground movements. These bearings are critical components for transferring dynamic load during taxi, takeoff, and landing. The bearings also ensure that the aircraft is mechanically strong enough to handle sudden vertical loads during irregular landings or ground movements, lateral loads during turning, or longitudinal loads from braking.

Credit: Airbus

Airbus recommends precautionary maintenance measures whenever damage is possibly found in the wheel bearings. That includes any deformation or rotational friction found after inspection. The use of proper cleaning agents and lubrication with lithium-based grease is also highly recommended by Airbus. Although clay-based grease is acceptable, Airbus studies have shown that lithium-based grease is much more effective at repelling water and contamination.

Airbus emphasizes that when installing a new wheel bearing, it should be performed quickly to avoid contamination, and the use of a cone-shaped protector during both removal and installation is crucial to preventing damage during the process. Finally, using the proper torque for initial seating and preload application ensures that the axle nut will remain secure but not induce excessive friction that leads to premature wear and tear.