Light helicopters flying under visual flight rules are particularly prone to loss of control when the pilots are gradually deprived of sufficient external visual cues, a study commissioned by the UK Civil Aviation Authority (CAA) has established.
The study, carried out by research company Qinetiq for the CAA, says the problem is at its most acute in helicopters that have little or no natural or artificial control stability, because even experienced pilots can quickly become overloaded with the demands of maintaining attitude, navigation, height and speed while external visual attitude references are deteriorating.
The report considers about 700 case studies between 1975 and 2004, and refers to independent findings during analysis by the International Helicopter Safety Team, which has found that helicopter flight in degraded visual conditions emerged as a significant cause of accidents in the USA, Canada and a number of states within Europe.
In the UK, the CAA has found loss of control or controlled flight into terrain in degraded visual conditions to be the largest single cause of fatal helicopter accidents, and it says that the incidence is increasing, explaining: "Small helicopters are particularly vulnerable to the hazards associated with helicopter flight in degraded visual conditions as they are not generally equipped with automatic stabilisation equipment."
The report states: "This project has firmly established a direct link between flight safety, visual cueing conditions and helicopter handling characteristics. At the heart of the high accident rate is the inherent instability of many small and some medium helicopters which can rapidly lead to excessive pilot workload when attempting to fly in degraded visual conditions.
"An obvious step to reduce the accident rate would be to improve the handling qualities of these aircraft, but it is recognised that such a step would likely be impractical for many existing aircraft. Other means must therefore be found." Simple head-up instrument display is one suggestion.
The CAA observes: "Pilots still become lost when navigating by visual references at night," adding: "Pilots should be better trained to make informed decisions on whether to fly or not in marginal conditions, or when IMC [instrument meteorological conditions] are developing en route."
Source: Flight International
