Cooper VANS RV-6 N36VR

Summary

On 26 February 1999 at about 21:30 local time, a Cooper VANS RV-6 registered N36VR was involved in an accident near Vacaville, California, United States. 2 people were on board and one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

26 February 1999 at 21:30

Classification

Accident

Location

Vacaville, California, United States

Coordinates

38.4097, -122.0098

Aircraft

Cooper VANS RV-6

Registration

N36VR

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX99LA111

1 person had minor injuries.

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.

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

Read the full 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.

Quoted verbatim from the NTSB record.