Airbus Helicopters AS-350B2 N407EM

Summary

On 23 June 2014 at about 18:45 local time, a Airbus Helicopters AS-350B2 registered N407EM, operated by Eaglemed LLC, was involved in an accident near Texarkana, Texas, United States. 4 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

23 June 2014 at 18:45

Classification

Accident

Location

Texarkana, Texas, United States

Coordinates

33.5356, -94.1925

Aircraft

Airbus Helicopters AS-350B2

Registration

N407EM

Category

Helicopter

Year built

1986

Engines

1

Operator

Eaglemed LLC

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Idabel → Texarkana

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN14LA312

Nobody was injured.

The failure of the two fuel control unit drive bearings for reasons that could not be determined based on the available evidence, which resulted in an uncommanded engine acceleration and subsequent overspeed condition. Contributing to the accident was the pilot’s improper autorotation, which resulted in a hard landing.

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

Read the full NTSB narrative

The commercial pilot and two flight crewmembers were conducting an emergency medical services flight. The helicopter was in cruise flight when the pilot noticed that the rotor rpm had rapidly increased and that the high rotor aural warning had sounded. Despite troubleshooting efforts, the pilot was unable to reduce the rotor rpm, so he performed on autorotation to a field. During the subsequent run-on landing, the helicopter touched down hard. During the landing, the main rotors contacted and partially severed the tailboom. Disassembly of the fuel control unit (FCU) revealed that the two drive bearings that ensure drive integrity between the FCU and the fuel pump had failed. The failure of the bearings led to excessive wear in the races and degraded the drive shaft such that it could no longer provide positive drive to the FCU, which the FCU interpreted as an underspeed condition. This led the FCU to command more power to the engine and resulted in an engine overspeed condition. Metallurgical testing of the FCU drive bearings did not reveal the reason for their failure. As a result of this accident, the engine manufacturer adjusted the FCU bearing replacement schedule from a one-time replacement to replacement every 600 hours.

Quoted verbatim from the NTSB record.