What happened
On August 14, 2013, a Robinson R44 helicopter, registration VT-HPC, operated by Pinnacle Air, was performing a revenue flight from Godhara to an Ahmedabad helipad. The aircraft was carrying a pilot and three passengers. After completing several earlier flight sectors that day, the helicopter departed Godhra at approximately 12:10 UTC.
While cruising roughly six miles from its destination, the aircraft suddenly experienced intense vertical vibrations. The pilot attempted to mitigate the shaking by reducing airspeed and adjusting the cyclic, but the magnitude of the vibrations continued to increase, rendering the aircraft difficult to control. The pilot issued a "MAY DAY" call to Air Traffic Control and initiated an emergency descent. The helicopter performed a controlled, straight-and-level forced landing in the Gomtipur cemetery. Upon touchdown, a sudden jerk and creaking noise caused the airframe to tilt forward and to the left, resulting in significant structural damage.
The investigation
AAIB India investigators examined the wreckage and the maintenance history of the aircraft. The investigation focused on the mechanical failure of the rotor system and the circumstances leading to the emergency. Investigators analyzed the condition of the main rotor blades and the impact dynamics of the landing. The inquiry also reviewed the aircraft's instrumentation and the pilot's compliance with flight rules under Special VFR (SVFR) conditions.
Findings
- The primary cause of the severe vibrations was the in-flight de-bonding of the main rotor blade skin, which sheared off approximately one-third of the blade's span.
- This structural failure created a significant static and dynamic imbalance in the main rotor system.
- While the second main rotor blade remained intact, investigators found evidence suggesting that de-bonding was likely beginning to occur on that blade as well.
- The impact with the ground caused the main rotor blade to strike the tail boom, resulting in the separation of the tail boom, tail gear box, and tail rotor blades from the main airframe.
- The aircraft was operating under SVFR conditions; however, the investigation noted that the helicopter lacked VOR or ADF instrumentation, which are typically used for such operations.
- Despite the substantial damage to the R44, there were no injuries to the pilot or the three passengers, all of whom evacuated the aircraft safely.
Safety action
- The investigation recommended that more stringent inspections of Robinson R44 main rotor blades be conducted, particularly at outstations, prior to the issuance of a Certificate of Release to Service (CRS) before every flight.