Plans for European commercial single-engine operations under instrument
meteorological conditions or at night (SE-IMC/night) are progressing slowly and could be delayed further as regulators continue to study the inherent additional risks such flights pose to passengers.

More than 20 years after the initial proposals that would allow commercial SE-IMC/night operations, likely timing for regulatory approval is moving steadily to the right. The European Aviation Safety Agency (EASA) has published an independent assessment of the risks in SE-IMC/night operations, but it will be at least another 12 months before work begins on a necessary notice of proposed amendment (NPA) to the EASA basic regulation’s ops implementing rules (IR).

Undertaken by UK technical consultancy Qinetiq, the risk assessment concludes that SE-IMC/night flights should not be prohibited automatically. The bad news for proponents, however, is that further moves must wait for the basic IRs to be established, a process that could take another year. EASA is “planning to base future rulemaking on the [Qinetiq study] results,” an agency official told NBAA Convention News.

EASA inherited consideration of SE-IMC/night flight regulation from its Joint Aviation Authorities (JAA) predecessor. Several states–including some EU countries such as Denmark, Finland and Norway–already permit commercial SE-IMC under specified conditions.

Roughly equivalent to U.S. single-engine IFR operations, such European flights might have begun in 2010 had EASA accepted JAA safety data. Agency officials challenged SE-IMC/night information from operations outside Europe used in JAA considerations as not being representative of European conditions and circumstances.

EASA said SE-IMC/night proposal work requires separate rulemaking activity after it has issued an “opinion” on the EASA Ops IR next year. SE-IMC/night could be covered with other changes in the expected first amendment to EASA-Ops in 2010/11.

Industry aspirations to fly SE-IMC/night in Europe have a long and tortuous history, with some countries having adopted a decidedly conservative approach. Lobbyists had hoped to achieve approval for so-called “risk periods” of up to a cumulative 15 minutes in any flight–during which commercial passengers would have been exposed to possible loss of engine power while outside still-air gliding range of undefined alternative landing areas.

UK regulators, for example, do not accept “the concept of an in-flight ‘risk period’.” Asked how much better single-engine safety needed to be to achieve
SE-IMC approval, officials said they were not tied to “any particular fatal-accident rate” as being acceptable

Concluding that “at least some objections might be valid,” EASA dropped the previous JAA NPA in favor of a “full and objective” assessment. “It is necessary to identify all the risks and possible mitigating factors assuring that SE-IMC operations do not involve more risks than multi-engine IMC operations,” the agency said.

Accordingly, Qinetiq reviewed existing engine reliability data to verify that it was “statistically valid, balanced, applicable to the airplanes expected to be used in [such] operations, [and] reflect[ed] the specifics of the European region.” The study concluded that fatal SE-IMC/night accident rates from all causes should be “more remote than 4 x 106/flight hours,” this target providing a small improvement over twin-engine safety in comparable categories. Likewise, SE-IMC/night engine-failure fatal-accident rates should be more remote than 1.3 x 106/flight hours (that is, a third of the rate for all aviation accidents).

The study made recommendations on training, aircraft-certification testing and crew complement (calling for a copilot to help manage workload following loss of engine power). Considering post-engine failure risks and measures to reduce engine-failure and forced-landing risks, Qinetiq found only sparse data, with many databases not able to demonstrate the effect of night or IMC operations. Qinetiq therefore developed a theoretical risk assessment that considered likely outcomes of engine failure during  VMC, IMC and night conditions.

The study said it is possible to show hypothetically that the target engine-failure fatal-accident rate is achievable, subject to “individual circumstances” and several other caveats.

Achieving the target also requires “appropriate limitations on cloud ceiling and visibility, [operations] from and to suitable airfields, [and] the duration of risk periods when no landing site is within gliding range.” The study said ceiling restriction should be 500 feet (or minimum descent height for a nonprecision approach to specified airfields and runways), with visibility of at least 3,600 feet for aircraft with a maximum stall speed of 61 knots CAS in landing configuration.