What happened
On December 8, 1999, at 19:40 local time, a C-208 Caravan, registration PT-OHA, operated by TAF Linhas Aéreas S/A, departed from SBJP for SBRF. Approximately ten minutes into the flight, while in a climb phase, the aircraft experienced a significant loss of power due to an engine failure.
During the night flight, the crew attempted to return to the departure airfield but determined the distance was too great. They then attempted to reach the BR-101 highway, which was visible in the darkness, but were unable to reach the roadway. The pilot ultimately performed a forced landing in a wooded area approximately 250 meters from the highway. The two crew members sustained minor injuries, but the aircraft suffered severe structural damage, including irreparable damage to the engine, propeller, and left wing.
The investigation
CENIPA investigators examined the engine and propeller assembly, discovering that the gas generator turbine had failed due to overheating. Laboratory analysis revealed that the turbine blades had melted, causing a loss of efficiency. To compensate for this loss, the Fuel Control Unit (FCU) increased fuel flow, which further exacerbated the overheating process. This failure caused parts of the turbine blades to break off and strike the engine components, damaging the power turbine stator and thermocouples.
Crucially, the investigation found discrepancies in the temperature measurement system. The installation of the thermocouples involved improper torque and grounding, which resulted in the cockpit instruments providing inaccurate, lower-than-actual Interturbine Temperature (ITT) readings. Furthermore, investigators found that components replaced during a previous inspection (the Wire Harness and T5 Bus-Bar) did not match the serial numbers recorded in the engine's maintenance logs. The investigation also noted that the crew failed to execute the full emergency checklist, specifically failing to use the recommended 30-degree flap setting, which could have reduced the stall speed during the landing.
Findings
- Inadequate maintenance supervision: The operator failed to properly monitor and verify maintenance tasks, allowing the aircraft to operate with false temperature indications.
- Maintenance deficiencies: Improper installation of thermocouples and the use of unrecorded components contributed to the engine's inability to signal overheating.
- Deficient crew coordination: The crew did not follow established emergency procedures or checklists during the engine failure event.
- Organizational culture: A lack of flight safety priority within the company and a lack of effective emergency training for pilots were identified as contributing factors.
- Operational factors: The lack of a Ground Power Unit (GPU) during high-temperature starts likely contributed to hot starts that went undetected due to faulty instrumentation.