Wed, May 04, 2011
AD NUMBER: 2011-08-07
MANUFACTURER: Rolls-Royce plc (RR) RB211-Trent
875-17, RB211-Trent 877-17, RB211-Trent 884-17, RB211-Trent
884B-17, RB211-Trent 892-17, RB211-Trent 892B-17, and RB211-Trent
895-17 Turbofan Engines
SUBJECT: Airworthiness Directive 2011-08-07
SUMMARY: This AD results from mandatory
continuing airworthiness information (MCAI) issued by an aviation
authority of another country to identify and correct an unsafe
condition on an aviation product. The MCAI describes the unsafe
condition as:
In January 2009 a Trent 895
powered Boeing 777-200 aircraft experienced release of a low
pressure (LP) compressor blade which failed due to fatigue cracking
in the root section of the blade. The released blade (undercut root
standard) had received a part life processing to apply a
compression layer to the blade root (Service Bulletin SB
72-D672–Introduction of Laser Shock Peening (LSP)) and also a
part life upgrade to the retention feature lubrication system.
Investigation has revealed that the effectiveness of this upgraded
blade root lubrication coating system may be reduced dependant on
the extent of previous running with the earlier standard, leading
to increased blade root stress levels. In the specific case of the
released blade, a review of its in-service modification history has
shown that it operated for a relatively high number of flight
cycles prior to the compression layer processing and the new
retention feature lubrication system. A review of the Engine Health
Monitoring data has also identified it operated at high N1 speeds
compared to the Trent 800 fleet average N1 speeds. The combination
of these factors has resulted in increased fatigue life usage which
is considered to have led to crack initiation and propagation prior
to reaching the blades declared life limit. A review of all
in-service undercut/LSP standard Trent 800 LP compressor blades has
identified specific blades that carry a similar increased
susceptibility to cracking.
This AD is issued to mitigate the risk of possible multiple fan
blades failure affecting those blades identified as described above
which could lead to high energy non-contained debris from the
engine. This AD has been issued to prevent LP compressor blades
from failing due to blade root cracks, which could lead to
uncontained engine failure and damage to the airplane.
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