What happened
On April 26, 2007, a Bell 206B helicopter, registration PT-YBJ, was conducting an electrical line inspection flight near Poloni, Brazil. Approximately 20 minutes after departing from Votuporanga, the aircraft experienced a sudden loss of engine power.
In an attempt to maintain rotor RPM and preserve energy, the pilot executed an autorotative maneuver. During the approach, the aircraft struck a tree due to the presence of tall vegetation in the landing area. The subsequent impact with the ground was abrupt, causing the landing gear to fail. The helicopter then rolled along its longitudinal axis across the terrain, causing the main rotor assembly and the tail rotor system to detach from the fuselage. The pilot and two passengers sustained minor injuries, while the aircraft suffered severe damage.
The investigation
CENIPA investigators examined the engine and the aircraft's maintenance history. Testing of the engine revealed that an air line had been installed incorrectly; the ends of the tubing were reversed, which prevented the proper application of torque to the nut securing the line to the fuel controller. This improper installation led to a pneumatic leak. This leak compromised the pneumatic signal used to manage engine operation, causing the engine to automatically revert to idle mode, which was insufficient to maintain controlled flight.
Additionally, the investigation found that an Airworthiness Directive (AD 2006-26-04) regarding a mandatory component replacement had not been complied with. The investigation also noted that the operator did not have technical personnel accompanying the flight mission to perform pre- and post-flight inspections, which may have prevented the early detection of the leak.
Findings
- Incorrect installation of an air line caused a pneumatic leak, leading to the loss of engine power.
- Inadequate maintenance supervision allowed the improper tubing installation and the failure to comply with an active Airworthiness Directive.
- Inadequate mission planning resulted in a lack of technical support for the remote operation, hindering the detection of the mechanical issue.
- Pilot judgment contributed to the severity of the impact, as the choice of a landing site with tall vegetation necessitated a premature flare, leading to the collision with a tree.