DATE: April 15, 2003
AD #: 2003-08-52
This emergency airworthiness directive (AD) 2003-08-52 is sent to all owners and operators of GE Aircraft Engines (GEAE) CT7-9B turboprop engines. These engines are installed on, but not limited to Saab Aircraft AB 340B airplanes. [Note: it is also found on the S-92, Bell 214, CASA CN-235, and Sukhoi 80, among others --ed.]

Background

This emergency AD is prompted by reports of 12 compressor stall events that occurred over a six month period. This is in contrast to recent historical experience of four to six stall events per year.

The stall events have occurred on deceleration when transitioning from takeoff power to climb power. Of the 10 events under investigation, nine had the compressor variable geometry (VG)  rigged to the VG schedule N1. The manufacturer’s maintenance manuals and related service bulletins permit the compressor VG to be rigged to either the VG schedule N or the VG schedule N1. The VG schedule N provides a higher stall margin at the expense of a small reduction of engine performance margin as compared to the VG schedule N1.

Since 1992, the manufacturer has recommended that overhaul shops use the VG schedule N only. VG schedule N provides more stall margin on used engines, which inherently have a lower stall margin due to wear or deterioration. Other factors that contribute to lower stall margins include dirty compressors and the increased compressor clearances that occur during the first takeoff of the day. This condition, if not corrected, could result in a dual engine in-flight shutdown or power loss due to a compressor stall during deceleration from takeoff power to climb power.

This AD is issued under 49 U.S.C. Section 44701..., and is effective immediately upon receipt.

Please see the AD itself for additional information.

FMI (pdf): AD