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ASN Wikibase Occurrence # 167492
Last updated: 2 July 2019
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Date:23-JUN-2014
Time:13:45
Type:Silhouette image of generic AS50 model; specific model in this crash may look slightly different
Aérospatiale AS 350B2 Ecureuil
Owner/operator:Eaglemed Llc
Registration: N407EM
C/n / msn: 1906
Fatalities:Fatalities: 0 / Occupants: 4
Aircraft damage: Substantial
Category:Accident
Location:Near Leary, just west of Texarkana, Texas -   United States of America
Phase: En route
Nature:Ambulance
Departure airport:Idabel, OK
Destination airport:Texarkana, TX
Investigating agency: 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 runon 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.

Probable Cause: 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.


Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20140624X92949&key=1


Revision history:

Date/timeContributorUpdates
25-Jun-2014 05:24 gerard57 Added
25-Jun-2014 05:25 harro Updated [Aircraft type, Registration, Cn, Source, Damage]
29-Jun-2014 05:16 Geno Updated [Time, Location, Phase, Departure airport, Destination airport, Source, Damage, Narrative]
25-Aug-2014 22:17 Aerossurance Updated [Narrative]
29-Mar-2015 09:24 Aerossurance Updated [Source, Narrative]
17-May-2016 21:01 Aerossurance Updated [Phase, Narrative]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
29-Nov-2017 15:02 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Source, Narrative]

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