What happened
On November 19, 2016, a Bell 206B helicopter, registration HK3986G, operated by Drummond Ltda., was performing a corporate flight to transport two executives to the El Descanso Mine sector in Cesar, Colombia. While cruising at approximately 1,200 feet, the pilot noticed a low rotor RPM warning light and a subsequent drop in engine revolutions.
The pilot immediately initiated emergency procedures, attempting to maintain rotor RPM by adjusting the collective. After determining that power could not be recovered, the pilot selected a nearby road as an emergency landing site and began an autorotation. At approximately 300 feet above the ground, the pilot observed approaching trucks on the intended road and executed a 90-degree right turn to reach a clear field.
As the aircraft reached approximately 7 meters (23 feet) of altitude and entered the flare maneuver, the engine failed completely, triggering an "Engine Out" alarm and an audible warning. The helicopter performed a hard landing, causing the landing gear and the lower fuselage to break, which subsequently led to a fuel leak. All three occupants—the pilot and two passengers—evacated the aircraft safely and were uninjured.
The investigation
The GRIAA investigation focused on the engine's performance and recent maintenance history. Investigators discovered that roughly five weeks prior to the accident, a technician had performed unscheduled maintenance on the Pc Filter system to verify a component part number. This work was conducted without a formal work order.
During this unscheduled activity, a line connected to the Pc Filter—which transmits compressor pressure signals to the fuel control system—was not properly torqued. The investigation also examined the pilot's pre-flight inspection, which failed to identify that the witness marks (alignment lines) on the components were not properly aligned, indicating loose connections.
Findings
- The primary cause of the accident was an engine failure resulting from a loss of Pc pressure, caused by an improperly torqued line on the Pc Filter.
- The loss of pressure was a direct consequence of unscheduled maintenance performed without proper documentation or oversight.
- Maintenance activities were conducted outside of established programs without adequate control, recording, or supervision.
- The pre-flight inspection was deficient, as the pilot failed to notice the lack of alignment on the critical component lines.