Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9, DC-9-80, and C-9 (military) series airplanes, and Model MD- 88 airplanes, that currently requires an inspection to detect chafing on the FIREX pipe assembly of the number one engine; and either repair of chafed pipe assemblies or replacement of the chafed pipe assemblies with new pipe assemblies; and modification of the FIREX and the pneumatic sense pipe assembly clamp marriage. That AD was prompted by reports of incidents in which the pneumatic sense pipe chafed against the FIREX supply pipe of the number one engine. This action would revise the applicability of the existing AD to include additional airplanes and remove others. The actions specified by the proposed AD are intended to prevent chafing of the FIREX supply pipe, which could result in a hole in the pipe and consequently prevent the proper distribution of the fire extinguishing agent within the nacelle in the event of a fire.