What happened
On May 12, 1993, an Embraer 120, registration PT-SLI, operated by Rio Sul Serviços Aéreos Regionais S.A., was performing a scheduled flight from Porto Seguro to Rio de Janeiro. During the descent, the crew experienced an uncommanded torque increase on the right engine, which fluctuated significantly. As the aircraft approached Santos Dumont Airport, the right engine torque increased again from 39% to 64% while the aircraft was at 650 feet.
The aircraft arrived at the runway with a high approach speed of approximately 140 knots, significantly exceeding the calculated Vref of 110 knots. Additionally, the aircraft was in a flap 25 configuration, failing to meet the operator's specific requirement for flap 45 when landing on runways shorter than 1,700 meters. Upon touchdown, the pilot applied both normal and reverse thrust, but the aircraft failed to decelerate sufficiently. In an attempt to stop the plane, the pilot applied the emergency brake, which caused the wheels to lock and the tires to burst. The aircraft subsequently exited the runway, crossed a grassy area, and collided with the breakwater stones at the end of the pavement. The accident resulted in three minor injuries among passengers and one minor injury to the flight attendant, while the aircraft sustained severe damage.
The investigation
CENIPA's investigation focused on the mechanical reliability of the engine and the crew's decision-making. Flight Data Recorder (FDR) analysis revealed that while the pilots reported torque fluctuations at FL 145, the FDR showed more stable parameters during that specific phase, though it did confirm a significant uncommanded power increase on the right engine during the final approach. The investigation also examined the maintenance history, noting that the aircraft had experienced similar Electronic Engine Control (EEC) issues in the days leading up to the accident, including torque variations and EEC failures.
Engine inspections conducted by the manufacturer were unable to pinpoint the exact cause of the uncommanded torque increase. Tests on the propeller control unit and engine components did not reveal any specific mechanical failures that could explain the power surge. The investigation also reviewed the crew's cockpit coordination and adherence to operational procedures regarding landing configurations and approach speeds.
Findings
- Uncommanded power increase: The right engine experienced an uncommanded increase in torque during the final approach.
- Improper landing configuration: The crew failed to use the required flap 45 setting for the short runway.
- Excessive approach speed: The aircraft landed at approximately 140 knots, well above the target speed.
- Inadequate decision-making: The commander failed to execute a go-around or a single-engine landing procedure despite the unstable approach.
- Poor cockpit coordination: The commander did not effectively utilize the co-pilot to manage the emergency or communicate with the cabin crew.
- Improper use of emergency brakes: The application of the emergency brake at high speed led to wheel lock-up and tire failure.