Accident Zenith STOL CH 701 N128CF, Tuesday 5 April 2011

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Date:	Tuesday 5 April 2011
Time:	16:00 LT
Type:	Zenith STOL CH 701
Owner/operator:	Richards David Stanley Iii
Registration:	N128CF
MSN:	75203
Engine model:	Hirth 3701
Fatalities:	Fatalities: 0 / Occupants: 2
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	El Centro, California - United States of America
Phase:	Initial climb
Nature:	Private
Departure airport:	El Centro, CA
Destination airport:	El Centro, CA
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
The pilot reported that, during the initial climb after takeoff, the airplane sustained a partial loss of engine power and that he initiated a forced landing to a wet, muddy, wheat field. During the landing roll, the nosewheel of the airplane dug into the soft terrain and the airplane nosed over. A postaccident examination of the engine revealed that the No. 2 cylinder and piston exhibited signatures consistent with oil starvation. During disassembly of the engine oil pump system, the No. 1 shaft/bearing assembly for the oil pump system was intact and operational. The No. 2 drive coupling was found damaged, out of alignment, and not functioning. This condition would result in the oil supply system supplying oil at a sporadic rate, below minimal volume and pressure, which would result in oil starvation primarily to the No. 2 cylinder assembly.

Probable Cause: A partial loss of engine power during the initial climb after takeoff due to oil starvation because of the failure of the No. 2 oil pump drive coupling.

Accident investigation: