What happened
On December 30, 2012, a Bell 407 helicopter, registration VT-PHH, was performing a non-scheduled passenger shuttle service between Katra Helipad and Sanjhi Chhat Helipad in the Katra Valley, Jammu & Kashmir. The aircraft, operated by Pawan Hans Helicopters Limited, was carrying six passengers and a single pilot on its third flight of the day.
While approaching the Sanjhi Chhat helipad, the pilot heard a loud bang followed by an immediate loss of engine power and a significant drop in rotor RPM. The pilot responded by lowering the collective to maintain rotor speed and began a rapid descent. During this emergency, a FADEC warning was triggered. Seeking a suitable site for an emergency landing, the pilot performed an autorotation and managed to guide the aircraft to a sloping surface near a riverbed. The helicopter made a heavy landing without power, sustaining substantial structural damage. While all occupants survived, the pilot and four passengers sustained serious injuries.
The investigation
An inquiry conducted by the Committee of Inquiry examined the engine components and the pilot's training records. A detailed strip examination of the engine, performed at a Rolls-Royce facility in the USA, revealed that the 3rd stage and 1st stage turbine wheels had burst. The investigation focused on the sequence of mechanical failures and the operational procedures in place at the time of the accident.
Findings
- The primary cause of the engine failure was the high cycle fatigue (HCF) failure of a single 3rd stage turbine blade at the trailing edge hub location.
- This initial blade failure caused the remaining 3rd stage blades to fracture due to overload, which subsequently led to the failure of the turbine-to-compressor coupling and a subsequent overspeed burst of the 1st stage turbine wheel.
- The pilot successfully managed the emergency by executing an autorotation and identifying a landing site, preventing a more catastrophic outcome.
- The investigation noted that the operator's Standard Operating Procedures (SOP) lacked a supplemented map or sketch of identified forced landing fields within the operational sector.
- It was also established that the pilot had not completed required simulator refresher training for critical emergencies, such as engine or system failures, as mandated by regulatory requirements.
Safety action
- The operations department of the operator is required to ensure that pilot training for critical emergencies, including engine and tail rotor failures, complies with all applicable regulatory requirements.
- There is a need to identify and circulate specific, unobstructed flat landing areas to operators performing perennial services in the Katra region to assist in emergency planning.