Pilot, aircraft changes needed for safer low-visibility flying
The UK civil aviation authority (CAA) is recommending prevention and mitigation action to reduce the number of helicopter accidents in poor visibility. Proposed improvements include pilot guidance on whether to fly and better handling qualities. Together, controlled flight into terrain (CFIT), spatial disorientation and loss of control form the largest single cause of small-helicopter fatal accidents in the UK.
The UK has experienced a continuing incidence of serious civil helicopter accidents attributed to loss of control in degraded visual conditions over the last 30 years, according to CAA research project manager David Howson. Crash investigators have found many such accidents are associated with VFR flight “with the surface in sight.”
Current rules define this as “sufficient surface [...] to enable the flight crew to maintain the aircraft in a desired attitude without reference to any instrument.”
Accident reports indicate that pilots were often right in their decision to initiate flights, Howson explained, but problems stemmed from deteriorating visual conditions en route. He maintains that a review of operating minimums is an essential part of accident prevention, hinting at a visibility minimum of 10,000 feet, a little less than two miles. However, he concedes that a minimum is effective only if pilots follow the rule.
He further proposes that pilots be provided with guidance to help them with the go/no-go decision. One possible form of guidance is a risk factor checklist. As an example, Howson listed 12 risk factors a pilot should consider when planning a VFR flight with the surface in sight. Experience shows that pilots should opt not to fly when factors one to nine are ticked. These include, among others, “a segment of the route involves flying over a rural, unpopulated area,” the pilot is not trained for unusual attitude recovery and significant layers (4/8 to 8/8) of low-level clouds are likely to be found en route.
Howson also recommends that the manufacturers implement mitigation measures. He contends that handling qualities requirements for IFR “would significantly enhance safety.” For example, undamped responses, as opposed to attitude-command/attitude-hold responses, increase pilot workload. As a result, the threat of loss of control is greater with undamped responses.
Another mitigation action would be a requirement for an attitude indicator for all operations. Crews would be trained to use it in recovering from flight in degraded visual conditions, such as inadvertent IMC.