Accident Avro 504K N4929, Saturday 17 October 2009

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Date:	Saturday 17 October 2009
Time:	14:05 LT
Type:	Avro 504K
Owner/operator:	Rhinebeck Aerodrome Museum
Registration:	N4929
MSN:	HAC1
Total airframe hrs:	207 hours
Engine model:	LERHONE TYPE C
Fatalities:	Fatalities: 0 / Occupants: 1
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	Rhinebeck, New York - United States of America
Phase:	Initial climb
Nature:	Demo/Airshow/Display
Departure airport:	Rhinebeck, NY (NY94)
Destination airport:	Rhinebeck, NY (NY94)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
The pilot was performing an aerial demonstration for spectators. Shortly after takeoff, he heard a 'thump,â€ the engine lost power, and he performed a forced landing in trees. Post-accident inspection of the wreckage revealed a keeper and cotter pin that connects the push rod to the number 3 cylinder valve rocker arm was missing. The high-tension spark plug lead to the number 5 cylinder was severed. The pilot, who also maintains the aircraft, believes the flailing spark plug lead flew into the commutator ring, shorting out other cylinders and leading to a total power loss. The missing hardware from the number 3 cylinder was never recovered. According to maintenance records, the airplane received a condition inspection on September 22, 2009. During that inspection, the number 5 cylinder was removed for repair and reinstalled, and the other rocker arms and valve springs were inspected.

Probable Cause: A loss of engine power due to the in-flight separation of the number 3 cylinder valve rocker arm attachment hardware. Contributing to the accident was the improper maintenance inspection of the engine.

Accident investigation: