Olson SONEX N478SX

Summary

On 21 November 2004 at about 20:30 local time, a Olson SONEX registered N478SX was involved in an accident near Oconomowoc, Wisconsin, United States. One person was on board and one was seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

21 November 2004 at 20:30

Classification

Accident

Location

Oconomowoc, Wisconsin, United States

Coordinates

43.1094, -88.4861

Aircraft

Olson SONEX

Registration

N478SX

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Watertown → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CHI05CA032

1 person was seriously injured.

The loss of engine power due to a fatigue fracture of the crankshaft. An additional cause to the accident was the pilot/builder's failure to verify the dimensions of the shrink-fit crankshaft components prior reassembling the engine. A factor to the accident was the ditch encountered during the forced landing.

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

Read the full NTSB narrative

The amateur-built airplane was damaged during a forced landing following a loss of engine power during cruise flight. The propeller and hub separated in-flight as result of a crankshaft failure. The airplane impacted a small ditch during the forced landing that resulted in the airplane nosing-over. The experimental airplane was powered by a non-certified Volkswagen 2180cc engine that was modified for aircraft use. The engine crankshaft was fractured between the oil-slinger and the retaining snap-ring groves. The fracture initiated at the aft edge of the forward keyway. The fracture features were consistent with a fatigue-type failure. The propeller and hub were not recovered during the investigation. The pilot/builder reported that he had mistakenly installed the number four (aft-most) bearing at the number two position during initial assembly of the engine. He had to remove the shrink-fit propeller hub, drive gears and spacer in order to reinstall the bearings in the correct order. The pilot/builder reported that he did not check the dimensions of the shrink-fit components prior to reassembling the engine, nor did he consult with the engine kit manufacturer on how to disassemble, inspect, and reassemble the engine components. The engine kit manufacturer did not provide the builder with engine disassembly or overhaul instructions with delivery of the engine kit. The engine kit manufacturer did not instruct builders to verify the dimensions of the shrink-fit components prior to their installation. The experimental airframe and engine did not have to comply with federal regulations required for a standard category airplane. The engine and airframe had accumulated 45.3 hours since new.

Quoted verbatim from the NTSB record.