Wed, Apr 16, 2003
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.]
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
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
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