What happened
On 31 March 2022, a Ryanair Boeing 737-8AS, registration EI-DLC, landed at Adolfo Suárez Madrid-Barajas Airport following a flight from Brindisi, Italy. During the taxi phase from the runway to the apron, the crew noticed an unusual deceleration. Despite applying engine thrust to maintain speed, the aircraft's velocity dropped significantly, eventually coming to a rapid stop on the M25 taxiway without the use of brakes.
Upon inspection by ground personnel, it was discovered that the left wheel on the left main landing gear was misaligned and making contact with the brake body. The incident involved no injuries to the 153 passengers or 6 crew members on board.
The investigation
The investigation focused on the mechanical failure of the landing gear and the maintenance history of the affected component. Analysis of the wheel manufacturer's data revealed that the hub of the inner wheel half had completely fractured.
Investigators examined the maintenance records of the wheel, which had undergone a major overhaul only two months prior to the incident. While the aircraft was up to date with all prescribed maintenance intervals, the investigation found that a specific non-destructive testing (NDT) task—intended to inspect the bearing bore—had not been performed because the bearing cup was not removed during the overhaul, as permitted by the then-current Component Maintenance Manual (CMM) revision 10.
Findings
- The primary cause of the incident was a fracture in the hub of the inner wheel half of the left main landing gear.
- The failure originated from a fatigue crack that propagated from a corrosion pit located on the chamfer between the bearing bore and the sealing surface.
- The crack was hidden from view by the bearing cup, making it undetectable during standard visual inspections.
- A contributing factor was that the maintenance instructions in CMM revision 10 were insufficient to ensure the integrity of the wheel, as they did not mandate the removal of the bearing cup for inspection unless other anomalies were found.
- The wheel manufacturer has since updated the CMM (revision 13) to include ultrasonic inspections to detect such cracks.