Newly certified Part 25 airplanes are the subject of FAA rulemaking that revises the requirements for protecting fuel tanks and related systems from lightning strikes. This action, based on a 2014 notice of proposed rulemaking, is effective on November 19. Besides new type certification (TC) applications, the rules also apply to amended TCs and/or STCs for “significant-level change projects,” the agency said.

The new rules relieve manufacturers of several burdensome requirements, notably removing the mandate for manufacturers to provide triple-redundant fault tolerance in lightning protection. It also eliminates regulatory inconsistency by establishing a single standard for lightning protection of both fuel tank structure and fuel tank systems.

Further, the rule establishes a performance-based standard that the design and installation of fuel systems “prevent a catastrophic fuel tank explosion” by lightning and its effects. This performance-based standard allows applicants to choose how to provide the required level of safety.

This action also enacts airworthiness limitations to preclude the degradation of design features that prevent catastrophic fuel vapor ignition caused by lightning. Its intended effects are to align airworthiness standards with the industry’s and FAA’s understanding of lightning, as well as address issues of inconsistency and impracticality that applicants experienced with previous lightning protection regulations. Finally, the rule eliminates the need for the FAA to issue special conditions and exemptions.