What happened
On March 1, 2001, a Bell 206B helicopter, registration ZS-HKE, was conducting a private flight from a farm in the Dwaalboom area toward Rand Airport. While cruising at an altitude of approximately 6,000 feet, the pilot noticed a smell inside the cabin resembling an electrical fire. This was followed by the sight of smoke emerging from the overhead electrical and circuit breaker panel.
Following the appearance of smoke, the 'ENG OUT' audio warning activated and the corresponding light illuminated on the annunciator panel. Fearing an active in-flight fire, the pilot deactivated both the battery and generator switches. After identifying a suitable open field, the pilot reduced the throttle to idle and initiated an auto-rotational descent. The aircraft struck the ground at a high rate of descent, causing the main rotor blades to strike the tail boom and sever it from the airframe. The engine remained running after the impact, and the pilot eventually shut it down manually. There were no injuries among the three people on board.
The investigation
Investigators examined the aircraft and the circumstances surrounding the cockpit warnings. While the pilot reported an electrical fire smell and smoke, the investigation could not find physical evidence to confirm the specific origin or cause of the smoke in the cabin.
Findings
- The pilot's decision to deactivate the battery and generator switches was prompted by the perceived threat of an electrical fire.
- Following the deactivation of the electrical systems, the pilot observed the Turbine Outlet Temperature (TOT) gauge dropping. This led to the misinterpretation that the engine had failed, which triggered the decision to perform the auto-rotational landing.
- The engine had not actually failed, as evidenced by the fact that it was still operational at the time of impact.
- The engine sustained damage from foreign object debris (FOD) ingested during the landing.
- The high rate of descent during the landing caused the main rotor blades to impact the tail boom and tail rotor drive assembly, resulting in the structural separation of the tail boom.