What happened
On April 8, 2014, an Ecureuil AS 350 BA helicopter, registration VT-MAB, operated by M/s Mesco Aerospace Ltd., was performing a charter flight from Muradnagar to Manakmau. While cruising at approximately 2,000 feet AGL, the crew experienced intense, high-frequency vibrations. As the instability worsened, warning lights for the tail gear box (TGB) and the cabin door illuminated.
In response to the deteriorating flight conditions, the pilot initiated a straight-in autorotation. The aircraft landed in an agricultural field in Chakwali village, near Saharanpur, Uttar Pradesh. While there were no injuries to the two crew members or the three passengers on board, the helicopter sustained significant structural damage during the impact. The aircraft skidded and bounced upon hitting the ground, resulting in damage to the tail boom, tail cone, and tail rotor blades.
The investigation
An inquiry committee examined the wreckage and maintenance records to determine the origin of the mechanical failure. Technical analysis of the components, which included examination by the BEA in France, focused on the tail rotor assembly. Investigators scrutinized the maintenance history of the aircraft, noting that while the helicopter was under a continuous maintenance program, certain discrepancies were identified in the documentation and specific inspection intervals.
Findings
- The primary cause of the incident was the fatigue failure of a tail rotor pitch change link.
- Detailed examination revealed that the bearing ball within the pitch rod exhibited wear and play, which likely led to the fatigue rupture of the housing.
- The failure of this link caused lateral movement in the tail rotor, leading to the cracking of a tail rotor blade and subsequent damage to the tail boom and vertical stabilizer.
- A contributing factor was the pilot's inability to reduce the aircraft's airspeed to the recommended 65 knots for autorotation due to the extreme vibrations. The pilot performed the landing at approximately 80 knots, which resulted in a hard impact and subsequent structural damage.
- Investigators also noted that the monthly functional checks for the Emergency Locator Transmitter (ELT) were not being performed by the operator.
Safety action
- A safety audit of the operator's maintenance activities was recommended to be conducted by the DGCA.
- It was recommended that the flight crew receive appropriate corrective training.