AS 350 crash prompts review of flight procedures

 - March 30, 2009, 6:32 AM

The UK’s Air Accidents Investigation Branch (AAIB) issued four safety recommendation as a result of the Sept. 15, 2007 fatal crash of a Eurocopter AS 350B2 Squirrel in Lanark, Scotland. The accident killed all four aboard–the pilot (world champion rally car driver Colin McRae), his young son, a friend of the son and an adult friend of the family.

According to witnesses, including two who had military and civil helicopter experience, the helicopter–a familiar sight in the area–was flying faster and lower than usual before it descended into a valley near the pilot’s home. Although there were no witnesses to the accident itself, the adult passenger had been using a camcorder for much of the flight and this showed that the passengers had been enjoying low flight with some spirited maneuvers.

The AAIB investigating team failed to establish any mechanical failure, but the report acknowledges that the board could not entirely rule out such a failure. Soon after entering the valley the helicopter made contact with two large trees and received severe damage to the rotor head, causing a complete blade to detach and fly nearly 500 feet to a nearby field. Marks on the trees indicated that the pilot might have been trying to recover from a track deviation caused by a tailwind in the well-wooded valley.

Investigators also considered that he could have suffered from spatial disorientation, pure misjudgment or possibly a “jack stall” situation. Jack stall means that if the aerodynamic forces on the rotor blades become too large, these forces overpower the hydraulic system and the flying controls become heavy to operate. This can give the pilot the impression that the controls are jammed, and if he or she does not restrain them the helicopter will roll to the right and may pitch up. Substantial input force from the pilot is required to override this situation. The AS 350B2 Flight Manual warns pilots not to exceed relatively low flight load factors (2.2g at 120 knots).

The final report included four safety recommendations, three of which cover awareness of the symptoms, hazards and recovery procedures through entries in flight manuals and training during helicopter type conversion. The final recommendation regarded the checking of pilot’s licenses, as McRae’s had been expired for nearly two years.