History of Flight
On November 29, 2016, at about 0850 central standard time, a GoJet Airlines Bombardier CRJ700, registration N367ACA, experienced an uncontained failure of the No. 1 (left) engine while cruising at flight level 340. The aircraft was powered by two General Electric CF34-8C5B1 turbofan engines. The crew reported hearing a loud noise from the rear of the airplane, immediately followed by a rollback and flameout of the No. 1 engine. The crew declared an emergency and diverted to Lambert-St. Louis International Airport (STL), where they executed an uneventful single-engine landing. The flight was operated under 14 Code of Federal Regulations Part 121 as a regularly scheduled Delta Air Lines connection from Cincinnati/Northern Kentucky International Airport (CVG) to Denver International Airport (DEN). There were no reported injuries to passengers or crew.
Damage to Airplane
The airframe sustained no damage. Examination of the No. 1 engine revealed a penetration in the low pressure turbine (LPT) case; however, the released debris did not penetrate the engine nacelle.
Investigation Findings
The incident engine, serial number E965352, was shipped to Delta TechOps in Atlanta, Georgia, for disassembly. The LPT case penetration was located at the 8 o'clock position, about 1 inch aft of the LPT flange, coinciding with the high pressure turbine (HPT) 2nd stage rotor plane. Case material around the penetration was curled radially outward. Seven HPT 2nd stage blades were found separated below the blade platform, while the remaining 61 blades exhibited impact damage and were separated above the platform at random locations. All four LPT rotor and nozzle stages showed impact and thermal damage.
Metallurgical analysis was conducted at GE materials laboratories. The seven blades that separated below the platform all fractured at the shank upper radius, with fracture surfaces showing visual evidence of high cycle fatigue originating from corrosion on the convex side. The 61 blades separated above the platform failed due to overload, consistent with secondary damage. Multiple blades among the 61 had corrosion and fatigue cracks below the platform in the same area as the seven blades. Blade material composition and hardness met drawing specifications.
The LPT case was examined at GE's Evendale, Ohio, facility. Case material composition and hardness were within specifications. The penetration fracture surfaces exhibited ductile dimples consistent with overload. The NTSB materials laboratory reviewed both GE reports and concurred with all findings.