(Bloomberg) -- Boeing Co. called out potential fire-safety issues with the fuel-tank design on Airbus SE’s coming 321XLR, a jet that’s crucial to the European planemaker’s future lineup.

Airbus has positioned the rear-center fuel tank of the A321XLR under the floor of the passenger cabin -- giving it the added range that makes the plane, due in 2023, such a threat to its U.S. rival.

In comments to the European Union Aviation Safety Agency, Boeing said that “fuel tanks integral to the airframe structure inherently provide less redundancy than structurally separate fuel tanks,” and could pose potential hazards in otherwise survivable off-runway events or landing-gear failures.

The submission from Boeing’s director of global regulatory strategy, Mildred Troegeler, was made in response to a consultation paper by EASA on Airbus’s plan to install insulation panels on the floor of the A321XLR.

While the panels would prevent passengers above the tank from getting chilled feet, Airbus says there isn’t enough room to install ones that fully meet existing standards for burn-through compliance.

It’s common for aerospace manufacturers to critique rival designs with regulators, given the intense competition and the importance of aircraft products. The A321XLR, announced in 2019, is crucial for Airbus, and is already eating into orders of larger planes. It’s timed to arrive just as long-distance travel is expected to ramp up again after the coronavirus pandemic.

Read: Airbus Is Aiming to Seize the Skies From Problem-Plagued Boeing

“As with any aircraft development program, Airbus is working hand in hand with the airworthiness authorities to fulfill all requirements for type certification,” Airbus spokesman Justin Dubon said.

EASA said last week that it agreed with Boeing’s concerns around the “structural crashworthiness” of the tank and the risk of fire due to heat transfer from an external threat. It will define compliance and protection measures in Special Condition documents, the agency said.

The regulator mandated the proposed Special Condition in a Jan. 18 filing. Airbus, based in Toulouse, France, will have to demonstrate that the central fuel tank will be as safe as the previous design of the basic aircraft, through tests, analysis supported by tests, or design similarity, EASA said.

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