What happened
On June 15, 2006, an AirOne Boeing 737-400, registration EI-COI, was performing a scheduled passenger flight from Catania Fontanarossa to Rome Fiumicino with 98 passengers and 6 crew members. During the 180-degree turn to align with runway 08, the crew felt an unusual jolt, which they initially attributed to runway irregularities. As the takeoff roll commenced, a passenger noticed a wheel separating from the aircraft and alerted a flight attendant.
Due to communication delays within the cabin crew, the flight deck was not immediately notified of the separation. The pilots, noting that the takeoff roll and liftoff proceeded without any cockpit warnings or unusual noises, continued the flight to Rome. During the flight, air traffic control confirmed that the missing wheel had been found on the runway at Catania.
Upon realizing the severity of the situation, the crew declared an emergency and requested a low pass over Rome Fiumicino to visually inspect the nose gear. Following the inspection, which confirmed only one wheel remained, the crew elected to land with the nose gear extended to prevent further damage from retraction and to reduce aircraft weight by burning fuel. The aircraft landed safely on runway 16L without further structural failure.
The investigation
The ANSV investigation focused on the structural integrity of the nose gear assembly. Technical examinations of the fractured axle revealed a two-stage failure mechanism. Macro-fractographic analysis showed a small area (approximately 5%) characterized by dark coloration and corrosion, representing the crack propagation phase, and a larger area (95%) showing characteristic "fish-scale" patterns indicative of a final dynamic brittle fracture.
Investigators examined the maintenance history and found that while all required inspections had been performed, the existing maintenance procedure (Corrosion Prevention Task Card P32-00-01) did not require the removal of a spacer. This prevented inspectors from seeing the area of the axle most subject to mechanical stress and prone to corrosion.
Findings
- The primary cause of the incident was the failure of the nose gear axle due to a stress corrosion cracking mechanism.
- The failure originated from generalized corrosion and pitting on the external surface of the axle.
- The crack developed in a high-stress zone that was not effectively inspected because the maintenance task card did not mandate the removal of the axle spacer.
- A delay in notifying the flight deck occurred because the cabin crew member deemed it inappropriate to interrupt the takeoff roll with the report.
- The crew's decision to continue the flight was based on the absence of cockpit warnings and the lack of immediate awareness regarding the wheel separation.