David Learmount/LONDON

A CRUCIAL European decision on airliner-cabin emergency-exit design, is expected to be announced on 12 December, is set to derail the US/European regulatory-harmonisation process. The European Joint Aviation Authorities (JAA) conclusion, by exploiting a regulatory loophole, may lead to a reduction of safety margins for passenger evacuation.

The controversial nature of the JAA decision, will be heightened by the fact that, if the verdict goes the way which industry sources predict, Boeing will be able to offer more seats in its new 737-X series, than it could have done with its planned emergency-exit format, if the same aircraft had been certificated several years ago.

Airbus will protest about any safety-margin degradation or tilting of the "playing-field" in Boeing's favour, given that its competing A320 series had to be certificated under the original interpretation of the rules.

JAA regulation director Yves Morier has confirmed that the planned 12 December announcement concerns the interpretation of an existing cabin-design certification regulation.

The JAA admits that, at a mixed industry/authorities meeting on the subject in Hoofddorp, Belgium on 13 November, a radical transatlantic divergence of opinion emerged. The US Federal Aviation Administration refuses to move from its original intent for the regulation, while the JAA favours exploiting an amendment allowing "an alternative emergency-exit configuration...provided that the overall evacuation capability is shown to be equal to or greater than that of the specified emergency exit configuration".

The FAA's approach is based on the previously unchallenged premise that, if an emergency exit were between two of the five regulatory benchmark sizes, calculations as to how many evacuating passengers it could handle were based on the standard for the smaller size. This interpretation, called the "step" rule, provided a built-in "additional" safety margin because exits were rarely precisely the minimum size for their category. The JAA-favoured "line" approach would allow additional seating for any increase above the exit-category minima. This, according to Airbus, sets a precedent allowing future aircraft-evacuation-design calculations, to go for precise targets with none of the existing margin for error. The FAA told the Hoofddorp meeting that the JAA interpretation is not what it had intended.

Source: Flight International