On October 9, 2005, a Cessna CITATION 650 (registration N175DP) operated by Marshall & Ilsley Corporation was involved in an aviation accident near Madison, WI. Investigators recorded the probable cause as: The inadequate design of the engine's interstage transition duct that yielded after the LPT stage 3 blades had separated and allowed the uncontained release of turbine debris. A contributing factor was the separation of a turbine blade. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise, pilots heard a bang and left engine lost power. Precautionary landing was successful. Examination revealed broken LPT 3rd stage blades with fatigue progressions; blades had known high-stress issue.
Event Description
The airplane was in cruise flight when the pilots heard a bang and the left engine subsequently lost power. The flight crew executed a precautionary landing, which was completed without incident.
Examination Findings
An examination of the left engine revealed a hole in the bottom of the cowling. The low-pressure turbine (LPT) 3rd stage blades were found broken. The interstage transition duct was bulged outward around the LPT 3rd stage and exhibited an almost 180-degree split in the bulged section at the bottom of the duct.
Metallurgical Analysis
Metallurgical examination of the broken blades identified one blade that displayed fatigue progressions. By part number, the broken blades had previously been identified as having high stresses that could lead to separation of the blade through the airfoil section. However, the metallurgical examination of the case and its material determined that it conformed to engineering drawing requirements and material specifications.