What happened
On 16 March 2011, at approximately 07:20 UTC, a Bell 412EP helicopter, registration A6-FLV, operated by Falcon Aviation Services, arrived at the PC03 Wellhead Tower helideck in the Zakum Field, United Arab Emirates. The flight, a non-scheduled air transport operation, was intended to pick up ten passengers and various equipment.
As the final passengers were boarding the aircraft, the crew heard a loud noise. The helicopter suddenly settled and shifted into a nose-high attitude. The crew immediately shut down the engines and directed all passengers and crew to disembark the aircraft safely. Upon a subsequent inspection of the airframe, the crew identified that the undercarriage aft crosstube had failed.
The investigation
The GCAA AAIS investigation examined the structural integrity of the landing gear component and the maintenance history of the aircraft. Metallurgical analysis of the failed part, identified as part number D412-664-203, revealed that the fracture surface contained both fatigue beach marks and a region of fast fracture. The investigation confirmed that the component was made of Aluminium Alloy 7075 T6 and that no external damage or pre-existing stress risers were present on the tube surface.
Investigators also looked into the effectiveness of existing inspection protocols. They found that while the operator was following the manufacturer's instructions, the specific cracks were obscured by the layer of paint on the crosstube, making them undetectable through standard visual inspections.
Findings
- The primary cause of the structural failure was fatigue failure resulting from cyclic loading of the undercarriage aft crosstube.
- The existing fatigue cracks were not detectable during routine visual inspections because they were hidden beneath the paint layer.
- At the time of the incident, the specific part number involved did not have an assigned airworthiness life limit.
- There were no injuries to the 11 persons on board during the event.