Accident Eurocopter EC 120B Colibri N122TH, 26 Feb 1999
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ASN Wikibase Occurrence # 30750
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Type:Silhouette image of generic EC20 model; specific model in this crash may look slightly different    
Eurocopter EC 120B Colibri
Owner/operator:American Eurocopter Corp.
Registration: N122TH
MSN: 1017
Fatalities:Fatalities: 0 / Occupants: 1
Other fatalities:0
Aircraft damage: Substantial
Location:near Springtown, TX -   United States of America
Phase: En route
Departure airport:Grand Prairie, TX (GPM)
Destination airport:Amarillo, TX (TDW)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
While at cruise altitude, the helicopter's engine began to surge. The pilot initiated an autorotation to an open field. During the downwind forced landing, the skids dug into the ground, and the helicopter nosed over and came to rest on its left side. An examination of the engine revealed that the P3 air pipe, which supplies air to the fuel control, was broken close to the fitting on the combustion chamber casing. Examination of the P3 pipe revealed that its fracture was 'consecutive to the propagation of a fatigue fissure,' as a result of the pipe being 'subjected to an excessive vibratory excitation.' Engine vibration tests were conducted and two main excitation sources were identified. The two sources were the starter-generator and the breather gear assembly. The proposed solution to correct for this vibration consists of fitting an attachment clamp at mid-length of the P3 pipe, 'which moves the natural frequencies out of engine power ratings.'
Probable Cause: The improper touchdown executed by the pilot. Factors were the tail wind condition, and the manufacturer's inadequate design of the P3 pipe supports, which resulted in a fatigue fracture of the P3 pipe.



Revision history:

27-Sep-2008 01:00 ASN archive Added
25-Nov-2009 04:52 harro Updated
09-Mar-2013 12:58 TB Updated [Aircraft type, Location, Source, Narrative]
26-Nov-2017 10:00 ASN Update Bot Updated [Operator, Nature, Departure airport, Destination airport, Source, Narrative]

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