What happened
On September 5, 2010, a Cessna 208B, registration F-OIXZ, operated by Tropic Airlines, was performing a scheduled passenger flight from Pointe-à-Pitre to Saint-Barthélemy. Approximately eleven minutes after takeoff, while climbing through 7,000 ft, the pilot heard an explosion-like sound followed by a sudden loss of power. The engine stopped completely, and the propeller entered the feathered position.
At roughly 13 NM from the coast, the pilot attempted to return to the departure airfield but was unable to restart the engine. After declaring an emergency and notifying the passengers, the pilot executed an emergency landing in a sugarcane field at approximately 950 ft altitude. The aircraft struck the ground and slid for about 35 meters. The pilot and three passengers sustained light injuries, while the aircraft was heavily damaged.
The investigation
The investigation focused on the failure of the Pratt & Whitney Canada PT6A-114A engine. Investigators examined the engine components, specifically the compressor turbine (CT) stage. Metallographic examinations were performed on several blades, including blades 39 and 47.
Technical analysis of the fractured surfaces revealed multiple cracks parallel to the fracture sites. Microscopic examination of the blades showed the presence of microvoids and the complete dissolution of the gamma prime phase, which are characteristic indicators of material degradation. Previous borescope inspections had noted minor cracks on the cooling ring and coating loss on the CT blades, but these were within allowable tolerances at the time of the last inspection.
Findings
- The engine failure was caused by the rupture of one or more compressor turbine blades due to creep.
- The specific causes of the creep phenomenon could not be determined.
- The engine was equipped with older generation CT blades (P/N 3045741-01) which did not possess the improved creep resistance found in newer models introduced via Service Bulletins.