Cessna 650 Citation III, Madison, Wis., Oct. 9, 2005–The inadequate design of the engine’s interstage transition duct yielded after the low pressure turbine (LPT) stage-3 blades had separated and allowed the uncontained release of turbine debris, according to the NTSB. A contributing factor was the separation of a turbine blade.
N175DP was cruising at FL380 when the pilots heard a bang and the left engine lost power. The crew made a precautionary landing without incident. Ground inspection revealed an uncontained release of turbine material from the left engine, a Honeywell TFE731-4R-2S, which resulted in a hole in the bottom of the left engine’s cowling and numerous nicks and dents to the baggage door and the left side of the rudder. The two pilots and four passengers were not injured.
Metallurgical examination of the LPT stage-3 blades revealed faint fatigue progressions from the leading edge of one blade. In 2004, Honeywell had issued a service bulletin about LPT stage-3 blade separations advising their replacement at the next airframe Phase 8 inspection, the next major periodic inspection, compressor zone inspection, or the next time the LPT tie rod was unstretched, whichever came first. At the time the blade separation occurred, the incident engine had not reached any of the milestones in the service bulletin.