What happened
On June 18, 2003, at approximately 24:00 UTC, an Antonov An-124-100, registration UR-82029, was taxiing at Rome Fiumicino Airport following cargo operations. The aircraft, operated by the Antonov Design Bureau for a heavy-lift charter mission to Basra, Iraq, was maneuvering to reach the takeoff runway. While executing a right turn to enter taxiway 'A' from taxiway 'V', the right side of the nose gear strut failed.
The flight crew immediately implemented emergency procedures and brought the aircraft to a halt at the intersection of the two taxiways. The position of the heavy freighter obstructed traffic, necessitating the closure of the affected taxiways for approximately 20 hours. During the following night and morning, the crew unloaded the cargo and performed emergency repairs, which included removing the damaged strut and the right nose gear door to prepare the aircraft for a ferry flight.
The investigation
Investigators examined the aircraft on June 19, 2003. The inspection of the nose gear bay revealed that the right side strut had failed, causing minor damage to the fuselage structure and the left side of the gear bay. The inspection also noted that the hydraulic retraction actuator had been disconnected and temporarily secured with ropes, and various hydraulic lines and cables had been temporarily lashed to the airframe.
A detailed metallurgical analysis of the fractured right rotation arm was conducted. The fracture surface exhibited a circular crown pattern approximately 150 mm in diameter. The examination identified four distinct zones on the fracture surface: an area of stress corrosion cracking (SCC) characterized by corrosion pits and intergranular cracking; two areas of high-speed, instantaneous fracture (cleavage) with characteristic "fish-scale" striations; and one area of gradual, low-speed ductile deformation.
Findings
- The primary cause of the failure was fatigue cracking of the right nose gear strut rotation arm, which was initiated by stress corrosion cracking on the external surface of the component.
- Microscopic examination revealed that corrosion pits acted as stress concentrators, triggering the development of intergranular cracks.
- The fatigue crack progressed through repeated cyclic loading during landings and ground maneuvers, progressively reducing the effective load-bearing cross-section.
- The final failure occurred when the remaining structural section—reduced to approximately one-quarter of its original thickness—could no longer support the operational loads during taxiing.
- Evidence of oily residues on the fracture surface suggests that penetrant testing may have been performed during previous maintenance cycles, yet the crack progression remained undetected.