BELL OH 58C near Zebulon, GA — 2018-01-29

Probable cause

The pilot's failure to fully open the throttle before initiating the power recovery in response to a simulated engine failure.

NTSB narrative

The flight instructor was providing training to a student pilot during a local public flight. According to the flight instructor, during the fifth simulated engine failure of the flight, the helicopter throttle was advanced for the power recovery. The engine then accelerated, and the engine and rotor tachometer needles were in their normal operating range. At that time, the flight instructor initiated a climb. About 4 to 5 seconds into the climb, when the speed was about 25 knots and the helicopter was at an altitude of 125 ft above ground level, the engine lost power. The instructor made a forced landing into a field, which resulted in substantial damage to the tailboom. Postaccident examination of the helicopter showed proper throttle continuity and rigging as well as fuel system continuity. The engine was placed in a test cell, and the engine started immediately, accelerated smoothly, and ran continuously throughout the test protocol prescribed by the manufacturer. All measured performance parameters were within the manufacturer's acceptable range, which demonstrated that the engine, fuel control, and governor functioned as designed. The available evidence indicated that the throttle was likely not fully opened at the initiation of the power recovery and that, when collective pitch was applied, the fuel control (while governed) could not provide the fuel required to sustain the climb. A decay of engine and rotor rpm resulted, which likely led to the instructor's perception that the engine had failed and his subsequent decision to make a forced landing. The altitude and time available at the point of the perceived failure was likely inadequate to overcome the time requirements for throttle inputs and turbine lag.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Throttle position check before initiating climb could have prevented loss of power.

NTSB coding

• Loss of engine power (partial) · Autorotation

Evidence available

• Photos
• 8 docket documents

Docket documents8

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Instructor and Pilot's Statementinterview
• Mechanic Statementinterview
• Pilot's Statementinterview
• Statement of Party Representatives to NTSB Investigationinterview
• Photosphotos
• Rolls-Royce Engine Investigation Reportreport

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