Bell 47G N1159W accident near Wichita Falls, Texas

Probable cause

A total loss of engine power for reasons that could not be determined based on the available information.

NTSB analysis

The pilot reported that the purpose of the flight was to practice emergency procedures with a certified flight instructor (CFI). After completing four uneventful autorotations, they climbed the helicopter to an altitude of about 1,500 mean sea level and turned onto the final approach leg of the traffic pattern to conduct a ‘hydraulics off’ approach. Once established on final approach, the CFI reached down to turn off the hydraulic switch, and the engine lost complete power. The pilot immediately gave the flight controls to the CFI, and he prepared for an autorotation in a nearby field. During the descent, the helicopter impacted powerlines before it landed hard. The main rotor blade severed the tailboom, and the helicopter spun before it came to rest on its side.

The CFI confirmed that when he reached down to turn off the hydraulic switch, the engine lost complete power. He mentioned that the hydraulic switch is on the lower console, and he was unaware of any nearby switches that would have turned off the engine.

During a postaccident examination no anomalies were noted with the engine that would have precluded normal operations. The instrument panel was removed; the electrical wires were examined, and no abnormalities were noted. At the accident site, the ignition switch was found in the BOTH position. The ignition switch positions (RIGHT, LEFT, and BOTH) were tested and functioned normally. However, when the key was in the LEFT or RIGHT position, movement of the key would temporarily ground the switch. It was noted that a long keychain attached to the key extended over the hydraulics switch when the key was in the ignition.

It is possible that the CFI moved the keychain away from the hydraulic switch and, in doing so, could have caused the ignition switch to temporarily ground. Subsequently, the engine would lose complete power with no warning. However, this scenario would require the ignition switch to be either in the LEFT or RIGHT position because moving the ignition key while in the BOTH position did not cause the switch to temporarily ground. Since there is no evidence of the switch being in a position other than BOTH, the investigation was unable to determine the reason for the total loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR19LA019 for the full record.