What aircraft was involved and where did it happen?

The accident on 2013-08-07 involved a aircraft, registration PTYSM, at MACAÉ, RJ, BR.

What was the probable cause of the accident?

The engine fire was caused by the structural failure of the first-stage turbine blades due to thermal degradation and sulfidation, likely exacerbated by previous hot starts during operation.

Engine Fire Forces Aborted Takeoff of S-76A in Macaé

An engine fire on a Sikorsky S-76A forced an aborted takeoff at Macaé Aerodrome, resulting in minor aircraft damage but no injuries.

What happened

On August 7, 2013, at approximately 12:25 UTC, a Sikorsky S-76A, registration PT-YSM, was performing a takeoff from Macaé Aerodrome (SBME) in Rio de Janeiro, Brazil. The aircraft, operated by Omni Táxi Aéreo S.A., was configured to transport two pilots and two passengers to an offshore FPSO vessel.

During the takeoff roll, the flight crew observed that engine parameters were below expected values and elected to abort the flight. As the aircraft taxied toward the parking apron, ground mechanics signaled the crew that fire was visible in one of the engines. Simultaneously, the engine #2 fire warning light illuminated in the cockpit. The Pilot in Command (PIC) immediately deployed the onboard fire extinguisher and directed an emergency evacuation. All four occupants evacuated the aircraft without injury, though the aircraft sustained light damage to the engine nacelles and engine #2.

The investigation

The CENIPA investigation involved a detailed technical analysis of the Allison 2 .50-C30S engine at the Department of Science and Technology (DCTA). Investigators examined the fuel control unit, ignition system, and fuel lines, as well as chemical analyses of the aviation kerosene (QAV-1) and lubricating oil; all were found to be within standard specifications.

An inspection of the engine's debris detector revealed a significant amount of metal particles, which led investigators to examine the turbine section. The analysis revealed that the turbine blades had undergone thermal microstructural changes due to prolonged exposure to excessive temperatures. This degradation led to the development of cracks that eventually caused the failure of the blades on the first-stage turbine disk.

Findings

The primary cause of the engine fire was the failure of all blades on the first-stage turbine disk.
The blade failure resulted from thermal degradation and sulfidation (hot corrosion) on the aerodynamic profiles of the blades.
The microstructural changes in the blades were driven by exposure to excessive operating temperatures, which facilitated crack propagation.
The investigation noted that the engine had experienced "hot starts" during its operational history, a known factor in the degradation process.
The turbine assembly was operating at 1,646.7 hours since its last overhaul, which was below the manufacturer's 2,000-hour maintenance limit, indicating a premature failure.
The investigation could not determine if specific maintenance inadequacies contributed to the event.