Rhinebeck, NY, USA
N4929
PALEN AVRO-504K
The pilot was performing an aerial demonstration for spectators. Shortly after takeoff, he heard a “thump,” 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.
On October 17, 2009, about 1505 eastern daylight time, an experimental Palen Avro-504K, N4929, was substantially damaged after a loss of engine power and forced landing near the Old Rhinebeck Airport (NY94), Rhinebeck, New York. The exhibition airplane was owned and operated by the Rhinebeck Aerodrome Museum. The commercial pilot was not injured. Visual meteorological conditions prevailed at the time, and no flight plan was filed for the 14 Code of Federal Regulations Part 91 air show flight. The flight was originating at the time of the accident. The pilot reported that approximately 200 feet above ground level after takeoff, a “thump” was heard from the engine. He did not have sufficient runway in front of him for landing, so he turned to the right, away from the spectator line. The engine was losing power, so he attempted to maintain flying speed and set up for a landing on the runway. While turning base leg for runway 10, the engine continued to lose power and the pilot was forced to set the airplane down in the trees. He estimated the airspeed to be 35 to 40 knots when the airplane contacted the trees. An inspector from the Federal Aviation Administration (FAA) inspected the airplane following the accident. The wings sustained structural damage from contact with the trees. Examination of the Le Rhone 9-cylinder radial engine revealed that a push/pull rod that operates the number 3 cylinder intake and exhaust valves was disconnected. A keeper and cotter pin that connects the push rod to the valve rocker arm was missing. The missing parts were not located after a search of the accident site. The pilot, who also maintained the airplane, reported that his inspection of the wreckage revealed a high-tension lead on the number 5 cylinder spark plug was severed, presumably from being struck by the hardware that liberated from the number 3 cylinder. He added that, the “high tension lead broke free of [the] spark plug and flew into [the] commutator ring, shorting out more cylinders causing the engine to fail completely.” 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. The 1453 weather observation for Poughkeepsie, New York (POU), located 20 nautical miles south of the accident site, included the following: few clouds at 7,500 feet, surface winds from 360 degrees at 7 knots, 10 statute miles visibility, temperature 9 degrees Celsius, dew point 0 degrees Celsius, and an altimeter setting of 30.08 inches of mercury.
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.
Source: NTSB Aviation Accident Database
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