Single-engined public transport operations in IFR can now be made acceptably safe, making new services commercially viable

After deliberating since 1996, the European Joint Aviation Authorities is finally recommending a reversal of the rule forbidding commercial operations by single-engined aircraft under instrument flight rules (IFR). The 1998 advanced notice of proposed amendment (ANPA) has been modified to reflect industry input, and now has NPA status.

This snail-like pace seems strange given that in Australia, Canada and the USA such operations have been cleared and have not adversely affected safety. In the USA approval was more or less unconditional, because the Federal Aviation Administration thought it was the lesser of two risks - the risk of engine failure in a single-engined type versus the fact that "scud-running" under low clouds in an attempt to stay technically in visual meteorological conditions (VMC) was killing pilots and passengers in controlled flight into terrain accidents. In Australia the impressive engine reliability record of modern turboprop-powered single-engined aircraft such as the Cessna Caravan and Pilatus PC-12 led to rules specifying the types that may carry out single-engine IFR (SE-IFR) commercial work.

The most vociferous opponent among Europe's national aviation authorities has been the UK's Civil Aviation Authority. Its argument applies to UK conditions: UK weather is particularly fickle, and population density, particularly in the south east, is the highest in Europe, putting not just passengers but people on the ground at risk from forced landings carried out in instrument meteorological conditions, or at night. Even if the JAA finally gives the green light to the new regulation, it remains possible that the UK CAA will insist upon additional conditions before it allows SE-IFR in UK skies.

But the JAA is not proposing to go down the FAA's unconditional path. The NPA makes approval conditional on specified minimum power unit reliability statistics, and on additional equipment and training requirements. In fact, these conditions are so stringent that they make the mandatory minimum equipment list for unlimited extended range twin engine operations (ETOPS) in transcontinental airliners look undemanding.

The main rationale for the proposed reversal of the present ban is statistical data proving that the modern single-engined turboprops currently denied IFR operations already have a considerably better safety record than piston-powered twins that are accorded the privilege.

But regulators and the industry frequently claim that one of their prime aims is the improvement of flight safety, not merely its maintenance at present levels. So demanding realistic measures that lower the risk of power failure in already reliable aircraft is consistent with that aim; as is specifying equipment that will help a pilot to make the safest possible forced landing. And regulating in favour of single-engined commercial operations, for passengers in particular, represents a break with the mantra that all safety-critical aircraft systems should be fail-safe - usually achieved by providing back-up equipment. A single engine, by definition, does not have a back-up, so there have to be other ways to make it as reliable as possible.

Since no engine can be failure-proof, the JAA's approach is that the low risk of failure in approved machines must be further reduced. The NPA proposes that this should be achieved by fitting trend-monitoring equipment to the power unit as a whole - engine, gearbox and propeller - to monitor health and alert the pilot to a developing problem, enabling safe diversion.

For all the other aircraft systems, the NPA embraces the traditional fail-safe back-up philosophy. The JAA demands that standards never specified before for single-engined aircraft should be a requirement in types cleared for SE-IFR. This includes two independent electrical generation sources and powerful battery back-up that would give the pilot far more than just basic flight instrument data during an attempt to land safely in IMC.

The final aircraft provisions concern the fact that, occasionally, a forced landing away from an airfield may be the only option. The crucial demand here is that SE-IFR aircraft must have an area navigation system providing "approach accuracy" during the descent, and a capability to pre-programme it with en route locations that would be suitable for forced landings.

Taking account also of the NPA's pilot qualification and training requirement for SE-IFR, this is a well thought out proposal that deserves to be made a rule.

Source: Flight International