Rival planemaker Boeing told European regulators in 2021 the architecture of a fuel tank intended to increase the A321XLR's range "presents many potential hazards".

The FAA said in a filing it will require that the lower half of the A321XLR fuselage, spanning the longitudinal area of the tank, be resistant to fire penetration to protect passengers.

(Reporting by David Shepardson in Washington and Tim Hepher in Paris; Editing by Himani Sarkar)