Action
Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.
Summary
We are revising an earlier proposed airworthiness directive (AD) for all Rolls-Royce plc (RR) RB211 Trent 875-17, 877-17, 884-17, 884B-17, 892-17, 892B-17, and 895-17 turbofan engines. The NPRM proposed to require modification of the engine by removing any electronic engine control (EEC) that incorporates EEC software standard prior to version B7.2 and installing an EEC eligible for installation. The NPRM was prompted by failure of the intermediate pressure (IP) turbine disk drive arm and subsequent overspeed and burst of the IP turbine disk on an RR RB211 Trent turbofan engine. This action revises the NPRM by clarifying the costs of compliance, by clarifying that correction of the unsafe condition can be achieved either by installing upgraded software in the EEC or by installing an EEC with upgraded software incorporated, and by clarifying the installation prohibition statement. We are proposing this supplemental NPRM (SNPRM) to prevent overspeed of the IP turbine disk, resulting in failure of the turbine blades or the IP turbine disk and subsequent uncontained release of the disk and/or turbine blades, which could lead to damage to the engine and damage to the airplane.