Summary
We are revising an earlier proposed airworthiness directive (AD) for the products listed above. That second supplemental NPRM proposed a one-time inspection to determine the part numbers of the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines, and replacing affected aero/fire seals with new, improved aero/fire seals. That second supplemental NPRM was prompted by a report that the top 3 inches of the aero/fire seals of the blocker doors on the thrust reverser torque boxes are not fireproof. This action revises the second supplemental NPRM by prohibiting installation of certain non-fireproof thrust reverser seals. We are proposing this third supplemental NPRM to prevent a fire in the fan compartment (a fire zone) from migrating through the seal to a flammable fluid in the thrust reverser actuator compartment (a flammable fluid leakage zone), which could result in an uncontrolled fire. Since these actions impose an additional burden over that proposed in the second supplemental NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.