European safety regulators have proposed that the rear center fuel tank on the Airbus A321XLR must be designed so that in the event of a survivable crash, enough fuel would not be released near the fuselage or engine to cause a serious fire.
EASA said the current emergency landing certification conditions had to be supplemented given the tank’s “unusual design, location and installation aspects”.
EASA notes that the only guidance for protecting the fuselage tanks is based on an FAA advisory circular that focuses on auxiliary tanks that do not have any boundaries with the fuselage skin.
The regulator also noted that survivable accidents occurred outside of existing defined emergency landing conditions.
EASA is proposing a special condition for structural fuel tanks that in a survivable crash it must not release enough fuel to ignite a serious fire and conditions including runway excursion and loss of landing gear and engines with obstacles Collisions must be considered.
The regulator noted that tanks should be installed in areas that are “less likely to fail or rupture” under various impact scenarios, and suggested that applicants should consider incorporating features such as air pockets or crushable structures to mitigate impact and ground-scratching effects .
The tank integrity analysis should take into account parameters including a vertical descent rate of 23 ft/s, various fuel levels and payload conditions, while demonstrating that no hazardous fuel leakage results.
EASA added that airframe accident assessments should take into account pitch attitudes outside the normal envelope.
Sliding scenarios should examine yaw angles up to 20° at specific forward speeds. EASA said that sliding along the ground after various impact conditions should not cause the temperature inside the fuel tank to rise to the point of fuel ignition, or damage resulting in a serious leak.
EASA has published in February 2021 and in June this year special conditions for protection against penetration by external fire and special conditions for protection against ignition or explosion by vapors.