The FAA proposes to adopt a new airworthiness directive AD for all Airbus Helicopters Model EC 155B EC155B1 SA-365N SA-365N1 AS-365N2 and AS 365 N3 helicopters. This proposed AD was prompted by an engine compartment fire where the upper stiffener of the central firewall in the engine compartment was found damaged. This proposed AD would require replacing the aluminum central firewall stiffener with a titanium central firewall stiffener and prohibit installing an aluminum central firewall stiffener. These actions are specified in a European Union Aviation Safety Agency EASA AD which is proposed for incorporation by reference. The FAA is proposing this AD to address the unsafe condition on these products.