US regulators are formally seeking comment on proposed fire-safety conditions to accept the large aft centre fuel-tank design for Airbus’s long-range A321XLR twinjet.
The fuel tank – integral to the aft fuselage structure, with the top of the tank directly below the passenger cabin floor – is crucial to enabling the A321XLR to achieve its advertised 4,700nm range.
But the US FAA is concerned that the tank’s location and design means it is directly exposed to potential post-crash ground fuel-fed fires, unlike centre wing tanks or optional auxiliary centre tanks.
While the A321XLR aircraft is subject to several US requirements addressing fire safety of the fuselage and fuel tanks, these do not adequately deal with standards for post-crash performance of tank skin or structure – and the potential for the threat of external ground fire.
Although the FAA issued its proposed special conditions on 7 May, it says the requirements are “consistent” with previous special conditions drawn up by the European Union Aviation Safety Agency which were finalised in October last year.
As such the FAA’s proposal puts forward a requirement to prevent ignition of fuel vapour during an external fuel-fed ground fire, including accounting for possible hot-surface ignition created by that fire.
Airbus must demonstrate that the post-crash performance of the fuel-tank skin or structure is sufficient to allow safe evacuation should the aft centre fuel tank be exposed to a ground or pool blaze.
“The FAA would consider Airbus showing the design prevents ignition of fuel tank vapours in the integral [aft tank], during at least 5min of exposure to an external fuel-fed ground fire, as a sufficient time duration,” states the proposal.
It adds that this is consistent with analysis showing survivability is enhanced if fuselage burn-through is delayed by 5min.
“Airbus may consider a flammability-reduction system or ignition-mitigation means…when showing compliance with the proposed special conditions,” it states. The FAA is inviting comments on the proposed condition by 21 June.
