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16th of April 2015

A Swearingen SA 227-AC Metro III, powered by two Garret TPE331-11u-612g Turboprop engines, was operating a cargo flight between Riffle-Garfield County Airport and Denver International Airport (both in the state of Colorado, USA). The aircraft took off for the IFR (Instrument Flight Rules) flight at 22.37 local time.

One of the exit holes in the engine casing (Source & © Honeywell)

While climbing (and still below the tops of the mountains in the area) the pilot heard a loud "bang" and observed a yaw to the right. While indications that the right-hand engine had lost power and was on fire where indicated on the flight deck.

The pilot completed the required checklists and declared an emergency with ATC. Grand Junction Regional Airport (Colorado, USA) was the nearest suitable airport and a diversion was requested, and approved by ATC. ATC provided vectors for the single-engine instrument approach to Grand Junction where an uneventful single-engine landing was performed without any further problems. The aircraft taxied to a parking stand where the aircraft was shut down. A post-flight inspection of the aircraft revealed a large hole in the engine cowling. Further investigation revealed that the rotor of the second stage turbine had failed and one part had exited the engine casing and went through the left nacelle, after which it penetrated the righthand fuselage, coming to a rest inside the fuselage. Other parts of the second stage turbine rotor exited the engine casing and nacelle on the right-hand side of the engine and fell to the ground. There was no evidence of a fire in the engine area. The engine was removed from the aircraft and disassembled at a repair shop, where an examination of the 2nd stage rotor disk remnants revealed the presence of fatigue cracks which most likely caused the failure of the 2nd stage rotor. The 2nd stage rotor disk had accumulated 3901.4 hours and 4142 cycles. An investigation by the NTSB (their report is available by clicking here) concluded that the probable cause of the engine failure was;

"The uncontained engine failure was due to the fatigue failure of the second stage turbine rotor disk"

The incident aircraft (Source; Airliners.net © Conor J Ball)


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