The pilot of an MBB-Kawasaki (Eurocopter) BK117B2 flying a trauma recovery mission at 5,000 feet agl in South Australia last year saw a number of hydraulic fluctuations on the helicopter’s system indicators just before the aircraft experienced an uncommanded and violent pitch up. That excursion was followed closely by a left roll and descent, according to the Australian Transport Safety Bureau (ATSB).
The pilot instinctively pushed forward on the cyclic but was unable to regain control until the helicopter had descended to approximately 800 feet agl, at which point the pilot returned to the departure airport, Port Pirie. Nobody on board was injured, and the helicopter sustained only minor damage.
While the ATSB did not identify any mechanical issues as the cause of the hydraulic fluctuations or pitch up, the bureau did discover that the helicopter was being operated at a weight, density altitude and airspeed conducive to a stall on the retreating main rotor blade. Weather conditions were identified as an exacerbating factor. The ATSB said an uncommanded pitch up and left roll are characteristic of such a stall.
The ATSB later said the pilot’s pushing the cyclic forward delayed recovery from the stall and that this type of incorrect recovery could have resulted in a complete loss of control.