AD 91-21-01 R1 61 FR 29003 Active

This amendment revises an existing airworthiness directive (AD), applicable to Textron Lycoming Model TIO-540-S1AD reciprocating engines, that currently requires the upgrade of the engine exhaust system to a new design configuration; and also establishes inspection intervals for engines incorporating the new design configuration, for engines incorporating the design configuration required by a previous AD, and for engines not yet incorporating either design configuration. This amendment clarifies that an exhaust system disassembly is not necessary when inspecting the exhaust system after the installation of the new design One-piece Exhaust Riser Kit, and Manifold Retaining Kit. This amendment is prompted by reports from operators requesting clarification of two paragraphs in the compliance section. The actions specified by this AD are intended to prevent cracking or distortion of engine exhaust system flanges, V-band coupling, and pipes, which could result in engine compartment fire and smoke entering the cabin with possible loss to the aircraft.