WPR22LA174 · Bell Helicopter Textron Canada 407 HP

The pilot was performing a human external cargo (HEC) long-line qualification exam flight at the training operations facility of a public utility company. After performing the initial maneuvers, the pilot transitioned to the HEC phase of the exam by carrying a lineman on a 60-ft long line. While maneuvering the helicopter at an altitude of about 175 ft above ground level (agl), the helicopter lost engine power. In response, the pilot selected what he thought was the “emergency” throttle detent, but the engine did not respond. The pilot maneuvered the lineman away from the landing helicopter and performed an autorotation. The helicopter landed hard and sustained substantial damage. The pilot sustained serious injuries and the lineman sustained minor injuries.

A complete postaccident examination of the airframe, engine, and engine control systems did not reveal any evidence of preimpact mechanical malfunction or failures. The helicopter contained fuel, was loaded within its envelope, and weather was not a factor.

The engine was test run in a test cell and it performed nominally. Onboard video recorded a section of the annunciator panel that showed some, but not all, engine warning lights, none of which illuminated at any point during the flight. The recording did capture an audio tone as the descent began that was the same frequency as the engine out and low rotor warning indicators.

Review of data recorded by the engine control unit (ECU) revealed that at the time of the loss of engine power, the throttle was in the “IDLE” rather than the “FLY” position as would have been required during flight. A few seconds later, the throttle position moved back into the “FLY” range.

The pilot was flying the helicopter solo from the right seat with the door removed so that he could lean outside and observe below. The collective control, which housed the engine throttle twist grip at its end, was mounted on the pilot’s left side. The direction of throttle rotation meant that if the pilot maintained a tight grip on the throttle as he leaned right and out of the helicopter, the direction of throttle rotation was such that his hand could have inadvertently rolled the throttle out of FLY and into IDLE. Under this scenario, the engine would lose power immediately; both audio and engine diagnostic data confirmed this had likely happened. The pilot almost immediately rolled the throttle back into the FLY position but the design of the engine control system was such that it assumed the helicopter was on the ground and therefore limited power application to prevent an over-torque condition. So, even though the pilot immediately remedied the problem, the engine would not have regained power. The pilot stated as soon as he noticed a loss of power he moved the throttle beyond “FLY” and to the “emergency” position. However, although this position could be selected, it had no function on this type of helicopter; it was a hold out from the previous version of the helicopter that the pilot had flown. This mistake had no bearing on the accident and would not have affected the outcome.

The HEC operation required that the helicopter be flown at a low height and speed such that it was operating within the “AVOID” range of its Height-Velocity Envelope. In this range, a safe landing could not be guaranteed following an engine failure. Additionally, the nature of the training facility, with multiple training towers and obstacles in the immediate vicinity, further reduced the likelihood of a successful outcome in the event of an emergency. Therefore, although the pilot made the mistake of inadvertently shutting down the engine in flight, he was still able to demonstrate the presence of mind and helicopter control to maneuver the helicopter away from the lineman and into an open area.

This was the second time the pilot had taken the HEC exam, having failed the first attempt. The video recording appeared to show the pilot was anxious throughout the flight; however, considering the nature of the work he was performing and the stress he would have been experiencing, this is understandable. It could not be determined if this contributed to the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset