What happened
On December 29, 2008, a Sikorsky S-76A, registration PR-IME, was performing an offshore passenger transport flight from Macaé Airport (SBME) to the P-12 platform. The aircraft was carrying two pilots and seven passengers. During the takeoff roll, the flight crew noticed fluctuations in aircraft parameters and decided to abort the takeoff, performing a rejected takeoff with a landing roll on the runway.
After the aircraft came to a stop, the crew observed smoke emanating from the main transmission and engine area. The crew immediately shut down the engines and evacuated the passengers. Shortly after the evacuation, a fire intensified in the upper deck area, which was eventually extinguished by the airport's rescue and firefighting services. The aircraft sustained substantial damage to its electrical system, the upper deck components (including the main rotor, transmission, and engines), and the passenger cabin interior due to high temperatures.
The investigation
CENIPA investigators examined the wreckage and the aircraft's maintenance history. The investigation focused on identifying the ignition source of the fire. Investigators found that the fire originated in the electrical wiring of the Alternate Current Generator (AC GEN) located in the upper deck. This combustion was fueled by hydraulic fluid leaking from a nearby hose.
Physical examination of the hydraulic lines revealed that a pressure line hose had a loose connection and significant abrasion on its metal braiding. Additionally, the welding on the junction of the pin and nut of the pressure line hose was found to be broken and worn. The investigation also analyzed the electrical wiring, noting that the AC GEN utilized KAPTON insulation, a material known to become brittle and prone to cracking with age.
Findings
- Maintenance oversight: The investigation identified a lack of continuous maintenance analysis and supervision, as required by RBAC 135.431. Discrepancies in the hydraulic hoses suggested that maintenance quality was not being adequately monitored.
- Design and aging: The use of KAPTON insulation in the AC GEN wiring was a significant factor. As this material ages, it becomes rigid and prone to cracking during handling or through thermal cycling, which can lead to micro-current leakage and subsequent electrical arcing or flashover.
- Hydraulic leak: A leak in the hydraulic system, caused by worn and improperly maintained hoses, provided the necessary fuel to propagate the fire once ignition occurred.