Airbus and Boeing plead case for A380 and 787 exemptions

Airbus and Boeing have been forced to apply for exemptions to US Federal Aviation Administration certification rules that effectively limit the maximum cruising altitude of their respective A380 and 787 airliners to flight levels "well below 40,000ft [12,200m]", according to a petition filed by the US manufacturer.

A 1996 amendment to US regulations - originally targeted at rear-engined high-altitude business jets - introduced the requirement that the occupants of an airliner are never exposed to a cabin pressure altitude exceeding 40,000ft, or to an altitude exceeding 25,000ft for more than 2min, in the event of a decompression.

However, FAA rules also assume an extremely unlikely uncontained engine failure scenario, in which a one-third segment of the largest fan disc penetrates the fuselage tangentially.

The manufacturers claim this renders it impossible for any airliner with wing-mounted engines to operate above 40,000ft while meeting the decompression requirements contained in "amendment 25-87".

In its petition for the A380 to be exempted from amendment 25-87, Airbus says compliance "can only be achieved by restricting flight ceilings", because "when considering pilot reaction time and the heavy weight of an A380, it is impossible to reach FL250 [25,000ft] within two minutes after a rapid decompression occurs at maximum flight level".

It adds that European regulations permit operation of the ultra-large airliner at up to FL430, which will "enable the air traffic system to provide more capacity, and hence more aircraft separation and safety", and "provide for more economical operation of the A380".

The FAA has recognised the glitch and tasked its Aviation Rulemaking Advisory Committee to recommend changes, though adoption of any amendments could take several years.

In the meantime the FAA has provided guidelines to the manufacturers on how it will deal with applications for exemptions.

The new guidelines give new aircraft types more time to make an emergency descent to FL250 and eliminate the flight restriction above FL400. An aircraft flying at FL400 must be able to descend to FL250 within 2min 30s, or half-a-minute longer than the previous standard.

However, the FAA acknowledges that the medical community has criticised the new standard, citing "the lack of sufficient theoretical basis for this approach".

Airbus and Boeing have reason to be optimistic as the FAA has already granted an exemption allowing the Embraer 170 regional twinjet to operate at up to 41,000ft in US airspace.

The Brazilian manufacturer has lodged a similar petition for the larger 190 model.



Source: Flight International