What happened
On 17 July 2016, a Sud-Aviation SE-313B Alouette II, registration HA-PPC, was participating in a vintage aircraft fly-in at Breighton Aerodrome, Yorkshire. Following a period of several short flights, the pilot accepted four additional passengers for a final flight. During this flight, the pilot performed a series of maneuvers, including a zoom climb and a descent, before attempting a quick stop along the runway at approximately 55 knots.
As the helicopter performed the quick stop, the main rotor blades made contact with the tail boom structure. The impact caused the tail rotor assembly to separate and the engine to detach from its mounts. The aircraft rotated 180 degrees and dropped vertically to the ground. The pilot sustained fatal injuries, while the four passengers suffered serious injuries.
The investigation
The AAIB examination of the wreckage revealed that the main rotor blades had struck the tail boom, specifically impacting the stabilizer cross tube. This initial impact caused significant structural disruption, leading to the failure of the blade spacing cables and hydraulic dampers. The investigation established that the engine and transmission shafts underwent severe disruption, with one blade striking the engine with enough force to detach it from the airframe.
Investigators also reviewed the aircraft's weight and balance. Recent maintenance had increased the empty weight of HA-PPC by 46 kg, which shifted the basic center of gravity (CG) forward. Calculations indicated that with the added fuel and four passengers, the helicopter was likely at or above its maximum all-up weight of 1,588 kg, and the CG was positioned near the forward limit of the allowable range.
Findings
- The primary cause of the accident was the main rotor disc making contact with the tail boom structure during the quick stop maneuver.
- The aircraft was operating at or above its maximum allowable weight.
- The center of gravity was positioned towards the forward limit, which reduced the clearance between the rotor disc and the tail boom.
- Coarse control inputs during the dynamic maneuver likely contributed to the rotor disc striking the tail structure.