Helicopter controlled flight into terrain (CFIT) accidents occur mainly in daylight or visual meteorological conditions (VMC), reveals a new study by avionics manufacturer Honeywell. The company’s senior principal engineer Yasuo Ishihara has shown that popular preconceptions about the circumstances under which helicopter CFIT occurs are confounded by Honeywell’s analysis of the 66 US turbine-powered helicopter CFIT accidents between 1992 and 2003.

Speaking at the 7-10 November Flight Safety Foundation/Inter­­­­national Air Transport Association/International Federation of Air­worthiness safety conference in Moscow, Ishihara also revealed that the phase of flight in which most helicopter CFIT accidents occur (67%) is the cruise. Only 16% occurred on approach, 10% in manoeuvring flight, and 7% during the take-off phase. This, said Ishihara, is “counter-intuitive”, but it is what the statistics show.

Also non-intuitive, he said, is the fact that 52% of helicopter CFIT accidents occur in daylight, and 61% in VMC. Ishihara provided a breakdown of what the helicopters hit: 68% of impacts were with terrain, 28% with water, and 4% with man-made obstacles. The latter does not include hitting telegraph wires at low level.

US emergency medical service (EMS) helicopters, which have suffered an unusually high eight CFIT accidents in 2003-4, show a different accident pattern from those of turbine helicopter operations as a whole, said Ishihara. In US EMS operations, during the 1992-2004 period, 84% of CFIT accidents happened at night, but in 58% of the EMS accident flights VMC prevailed. Ishihara noted that night-vision goggles have been proposed as a solution, but said the fact that so many helicopter accidents occur in VMC and daylight show vision alone is clearly not the only issue.

Ishihara said helicopter terrain awareness and warning systems could supply the situational awareness that, according to the statistics, vision alone is not providing.


Source: Flight International