What happened
On 28 March 2011, a Bell 412EP helicopter, registration A6-FLZ, operated by Falcon Aviation Services, was at the Zakum West Super Complex (ZWAP) for a non-scheduled transport operation. After passengers had boarded the aircraft, the pilot heard a loud noise, and the helicopter suddenly settled into a nose-high attitude. The crew immediately shut down the engines and evacuated all 13 persons on board without injury.
The investigation
The GCAA AAIS investigation focused on the structural integrity of the aircraft's landing gear. Examination of the undercarriage revealed that the aft crosstube had failed. Laboratory evaluations identified that the failure was the result of metallurgical fatigue. The investigation also looked into the manufacturing history of the component and the effectiveness of existing maintenance and inspection protocols.
Findings
Technical analysis established that the primary cause of the incident was the fracture of the undercarriage aft crosstube due to metallurgical fatigue. Several contributing factors were identified:
- A manufacturing abnormality that resulted in inconsistent wall thickness within the crosstube.
- High levels of stress caused by cyclic loading on the component.
- The presence of multiple cracks that remained undetected during previous inspections because they were obscured by paint and their specific positioning.
- The existing inspection intervals and methods were insufficient to catch the fatigue before the failure occurred.
- The specific surface conditions of the landing area.
Safety action
Following the incident, several significant safety actions were implemented by various authorities:
- The landing gear manufacturer revised the fatigue analysis, established a 10,000-landing life limit, and introduced a mandatory liquid penetrant inspection (LPI) after 7,500 landings.
- Transport Canada Civil Aviation and the FAA both issued Airworthiness Directives to enforce a 10,000-landing life limit on the affected crosstubes.
- The operator proactively implemented a much stricter inspection interval, requiring an LPI every 2,500 landings.
- The GCAA received safety recommendations to standardize safety surface standards and non-slip material requirements for offshore helidecks operating within the UAE.