Robinson R44 II N544BS

Summary

On 24 June 2014 at about 17:35 local time, a Robinson R44 II registered N544BS was involved in an accident near Nashville, Tennessee, 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

24 June 2014 at 17:35

Classification

Accident

Location

Nashville, Tennessee, United States

Nearest airport

John C Tune (JWN)

Coordinates

36.2069, -86.8894

Aircraft

Robinson R44 II

Registration

N544BS

Category

Helicopter

Year built

2003

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Nashville → Decatur

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA14LA311

Nobody was injured.

The pilot’s failure to maintain rotor rpm during an autorotation after a perceived partial loss of power, which resulted in a hard landing. Contributing to the accident was radio frequency interference with the governor controller, which resulted in an uncommanded decrease in throttle and the perceived loss of engine power.

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

Read the full NTSB narrative

The pilot took off from his departure airport on a cross-country helicopter flight. The pilot reported that, when the helicopter was about 1 mile north of the airport and near a group of high-powered transmission broadcast towers, the engine started running roughly and that he felt an uncommanded decrease in engine power and movement of the twist grip throttle. The pilot initiated an autorotation, and the helicopter landed hard, which resulted in substantial damage to the tailboom. Postaccident examination of the engine revealed no mechanical anomalies that could have precluded normal operation. According to a flight instructor based at the departure airport, he had encountered a similar uncommanded decrease in engine power on multiple occasions while flying east of the same broadcast towers in the same make and model helicopter. During each encounter, the pilot felt the movement of the electronic governor through the throttle twist grip and was able to override the governor by advancing the throttle. Further, Federal Aviation Administration research revealed that high-power broadcast AM radio transmitters likely affect the governor circuit on this helicopter and can result in governor control that reduces the engine speed regardless of the pilot's power input. Thus, it is likely that radio frequency interference increased the engine speed signal frequency as the pilot flew the helicopter near the transmission towers. The governor controller then engaged the governor motor to decrease engine power, which the pilot perceived as a loss of power. About 15 years before the accident, the manufacturer had issued a safety notice to address previous reports of radio interference. The safety notice stated that flying near broadcast towers may result in "erratic operation of the governor," which may cause the governor to roll the throttle to the idle or open position. The notice also instructed pilots to keep one hand on the collective and throttle and to refrain from flying near broadcast towers. The pilot reported that he was familiar with the safety notice but that he had not read it since he purchased the helicopter about 7 years before the accident. The pilot should have been able to recognize that the engine was still producing power and overridden the governor by moving the twist grip throttle, and he should have been able to maintain rotor rpm while executing the autorotation, which would have resulted in a softer landing; however, he did not do so.

Quoted verbatim from the NTSB record.