What happened
On July 29, 2007, a Fokker F28MK0100, registration PR-OAU, operated by Oceanair Linhas Aéreas, was en route from Salvador, BA, to Rio de Janeiro, RJ. The aircraft was carrying 96 passengers and 5 crew members. During the initial climb, the crew noted a slight vibration, though all engine parameters remained within operational limits.
Approximately 20 minutes after takeoff, while cruising at FL280, the crew heard a loud bang followed by intense vibration. The cockpit instruments indicated high vibration levels in engine number 2, which subsequently failed. The pilots executed the appropriate emergency checklists and shut down the malfunctioning engine. The aircraft continued to Ilhéus, BA, where the crew successfully performed a single-engine landing. There were no injuries to the passengers or crew, though the aircraft sustained damage to engine number 2.
The investigation
CENIPA conducted the investigation with assistance from the German authority, BFU. Technical analysis of the engine (Tay 650-15) revealed extensive damage to the turbine assembly (module 5). Investigators found that the low-pressure (LP) turbine stator vanes at the first stage exhibited severe hot corrosion on their internal surfaces. This corrosion led to material thinning, cracking, and eventual loss of material.
The loss of material from the stator vanes allowed hot combustion gases to enter the hollow center of the vanes, impacting the interstage seal diaphragm. This impact caused thermal cracking and further material loss from the seal. The resulting debris struck the first-stage LP turbine rotor blades, causing them to detach and leading to subsequent mechanical damage in the second and third LP stages. This chain of events produced the intense vibration and the subsequent engine failure. Analysis of the Digital Flight Data Recorder (DFDR) showed no prior trends or malfunctions before the event, though a sudden drop in TGT was noted during the failure, likely due to thermocouple failure caused by the vibration.
Findings
- The primary cause of the engine failure was severe hot corrosion on the internal surfaces of the first-stage LP turbine stator vanes.
- The loss of stator material caused hot gases to damage the interstage seal diaphragm.
- Debris from the failing seal and stator vanes caused mechanical damage to the LP turbine rotor blades, leading to the engine failure.
- The engine had been previously stored in the Mojave Desert for over three years prior to its acquisition by the operator.
- It remains undetermined whether the corrosion originated from manufacturing defects, material handling, or maintenance/cleaning procedures during overhaul.