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ASN Wikibase Occurrence # 201973
Last updated: 16 June 2020
This record is based on the official accident investigation report. It has been locked for editing.

Date:26-FEB-1999
Time:13:30
Type:Silhouette image of generic RV6 model; specific model in this crash may look slightly different
Van's RV-6
Owner/operator:Private
Registration: N36VR
C/n / msn: 24999
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Category:Accident
Location:Vacaville, CA -   United States of America
Phase: Unknown
Nature:Private
Departure airport:O45
Destination airport:
Investigating agency: NTSB
Narrative:
The pilot made a forced landing into rough terrain following a bang and sudden loss of engine power. The engine had accumulated about 70 hours since overhaul. The sump contained a connecting rod, a wrist pin, bearings, many pieces of metal debris, and several rod cap bolts and nuts. None of the rod cap bolts in the sump were intact. They were all bent, fractured, and separated approximately at their midpoint. The pieces were covered with oil. The connecting rods for cylinders number two and four were leaning on the camshaft. The camshaft was not discolored. The crankshaft did not show evidence of discoloration or mechanical damage. A report of metallurgical testing of various engine pieces and their fracture surfaces strongly suggested that the nuts were not tightened on the connecting rod bolts according to specifications. A bolt that corresponded to the head of the bolt from cylinder number two exhibited failure characteristics of low cycle-high stress reverse bending fatigue. Reverse bending fatigue is indicative of an under-torqued bolt. The inspection revealed additional evidence that some of the nuts were not tightened to specification. Some bolts had flattened and polished bolt threads, as well as wear marks on the bolt's outer diameters. Some nut threads had only one end flattened. No fractured bolt had a nut on it except the fatigued bolt.
Probable Cause: The failure of the engine assembler to apply the proper torque on the connecting rods bolts, which led to fatigue cracking and ultimately fracture of the rod bolts.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001205X00196&key=1


Revision history:

Date/timeContributorUpdates
26-Nov-2017 10:01 ASN Update Bot Added