What happened
On November 13, 2003, a Bell 206L-4 helicopter, registration PT-YEE, operated by Helisul Táxi Aéreo Ltda., was performing a transport mission in the Amazon region. The flight began at the Porto Urucu oil base, destined for a clearing near the seismic exploration line 2051. After landing at the clearing to pick up passengers, the pilot attempted a second takeoff.
Shortly after clearing the treetops, the aircraft experienced a sudden loss of engine power. The pilot attempted to return to the landing site but was unable to maintain control. The helicopter struck trees and crashed into the ground. The impact triggered a fire, which was extinguished by personnel at the nearby camp. The accident resulted in two fatalities among the passengers, while the pilot and three other passengers sustained severe injuries.
The investigation
CENIPA's investigation focused on the mechanical failure of the Allison 250C30P engine and the operational procedures followed during the flight. Investigators examined the engine components and found significant carbonization within the internal parts. This carbonization, caused by lubrication system oil, led to friction between the N1 and N2 shafts, resulting in increased temperatures, material melting, and the eventual fracture of the shafts.
The investigation also scrutinized maintenance practices. There were indications that inspections might have been conducted at an unauthorized location (Porto Passarinho) without proper hangar facilities or infrastructure. Furthermore, the pilot failed to perform required takeoff performance calculations, as mandated by the company's General Operations Manual, due to the lack of specific weighing procedures for passengers and cargo at the time of boarding.
Findings
- The primary cause of the power loss was the rupture of the N1 and N2 shafts caused by excessive carbonization and subsequent friction.
- A contributing design factor was the high level of carbonization inherent to the Allison 250C30P engine model.
- Organizational issues were identified, including a lack of formal personnel selection and potential lapses in maintenance oversight due to inadequate inspection environments.
- The pilot did not perform required performance calculations prior to takeoff, increasing the risk during the critical climb phase.