Robinson R44 II N392GP

Summary

On 14 March 2013 at about 20:45 local time, a Robinson R44 II registered N392GP, operated by Leading Edge Aviation, Inc., was involved in an accident near Eagle Nest, New Mexico, United States. 2 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

14 March 2013 at 20:45

Classification

Accident

Location

Eagle Nest, New Mexico, United States

Coordinates

36.5572, -105.2553

Aircraft

Robinson R44 II

Registration

N392GP

Category

Helicopter

Engines

1

Operator

Leading Edge Aviation, Inc.

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

Dalhart → Monte Vista

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN13LA194

Nobody was injured.

A total loss of engine power due to a rapid throttle change during autorotation, which the flight instructor initiated in response to a low rotor rpm warning, which resulted from the separation of one of the magnets used to provide rotor rpm indications from the rotating transmission yoke. Contributing to the accident was the flight instructor's aft cyclic input upon landing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The flight instructor and student pilot were cruising about 800 feet above ground level when they heard a loud “bang,” followed immediately by the low rotor rpm horn, a warning light illumination, and a rapid decrease in rotor rpm indication. In response, the instructor initiated an autorotation by lowering the collective, and the engine immediately lost power. The helicopter touched down and then rocked forward due to soft and downward-sloping terrain. The instructor applied slight aft cyclic to prevent the main rotor blades from contacting the ground; however, the main rotor blades struck and severed the tail boom. The engine was functionally tested, and it operated normally. However, one of the magnets used to provide rotor rpm indications was missing from the rotating transmission yoke and was found affixed to a bolt just aft of the yoke. It likely had become loose in flight, and its movement was the bang heard by the pilots. Scarring was found on one of the sensors opposite the magnet, indicating that the magnet had contacted the sensor. The separation of the magnet caused the rotor rpm indication to drop and the low rotor rpm warning horn and light to activate. Due to the control linkage between the collective and the throttle, when the instructor lowered the collective, the throttle closed rapidly. According to Robinson Helicopters, rapid throttle changes can result in a fuel-air ratio becoming too rich or too lean to sustain engine operation and result in an engine failure.

Quoted verbatim from the NTSB record.