Flammability reduction means

This regulation requires Part 121 air carriers operating certain transport category turbine airplanes (those with 30+ passenger seats or 7,500+ pounds payload capacity) to install and maintain systems that reduce fuel tank flammability. These systems—called Ignition Mitigation Means (IMM) or Flammability Reduction Means (FRM)—help prevent fuel tank explosions.

New airplanes certificated after December 2010 must have these systems from delivery. Older airplanes required retrofits by December 2014 (50% of fleet) and December 2017 (100% of fleet), though all-cargo operations have different rules. Once installed, the systems must remain operational unless replaced with compliant alternatives.

Operators must also incorporate specific airworthiness limitations into their maintenance programs and get principal inspector approval for these changes. The regulation allowed one-year compliance extensions if operators committed to using ground air conditioning at gates when temperatures exceed 60°F.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*