Sedona, AZ, USA
N43064
Classic Aircraft Corp WACO YMF
The engine lost partial power during flight, and the airplane collided with a vehicle during a forced landing on a road. The pilot was performing a local for hire sightseeing flight for two passengers. Approximately 15 minutes into the flight, a loud "popping" noise was heard coming from the engine. The pilot was unable to maintain altitude and force landed on a city street. During the landing roll, the right wing impacted a car on the road. Post accident examination of the engine revealed that the number 7 cylinder exhaust valve rocker arm had failed in fatigue. The surface fracture initiation marks were consistent with a grinding operation during manufacture. The grinding operation is performed to remove any flash remaining at the mold parting line, after the casting operation, and is normally carried out by holding the part by hand and guiding it on a large grinding wheel.
On October 2, 2004, at 1025 mountain standard time, a Classic Aircraft Corporation WACO YMF biplane, N43064, lost engine power and collided with a vehicle during a forced landing on a city street in Sedona, Arizona. Solid Edge Aviation, d.b.a. Red Rock Biplane Tours/Safari Air Tours, was operating the for hire sightseeing flight under the provisions of 14 CFR Part 91. The airline transport pilot and two passengers were not injured; the airplane sustained substantial damage. The airplane departed from the Sedona Airport about 1000 for the local area sightseeing flight. Visual meteorological conditions prevailed, and no flight plan had been filed. According to the pilot, the tour was to be 30 minutes in duration. After approximately 10 minutes, the pilot heard a loud backfire and the airplane would not maintain altitude. The pilot glided down to a city street and prepared for landing. During the landing roll, the right wing struck a vehicle. The airplane was equipped with an onboard video recording system that was used to provide customers with a video record of their sightseeing flight. The video was sent to the National Transportation Safety Board Vehicle Recorder Division for review. Two cameras were mounted under the left wing. One was facing rearward with a view of the passengers, and the other camera had a view straight ahead of the airplane. One camera view was recorded at one time, and the video switched between the views approximately every 12 seconds. Audio was recorded through the airplane's intercom system. Approximately 15 minutes into the video recording, the engine made "popping" sounds. The pilot's narration of the flight ends mid-sentence and his voice was not heard for the remainder of the flight. The pilot proceeded toward a town [Sedona] and prepared for landing on a four-lane road with traffic. The engine continued "popping" as the airplane touched down. During the landing roll, the airplane appeared to strike an object, turned 90 degrees to the right, and then came to a full stop. Post accident examination of the airplane's engine revealed that the number 7 cylinder exhaust valve rocker arm was fractured. The rocker arm was sent to the Safety board Materials Laboratory for further examination. The rocker is constructed of a boss, which contains a bearing into which a rocker shaft is inserted, into two arms. One arm, identified as the pushrod arm, has a spherical seat into which the matching end of a pushrod is located, and the other arm, identified as the valve arm, has a roller that contacts the stem portion of the valve. The fracture was inboard of the pushrod arm portion where it connects to the rocker boss. Examination of the pushrod arm and boss portion displayed crack arrest marks of fatigue that matched each other. The metallurgist determined that the fracture surface marks were consistent with a grinding operation used to remove extra material (commonly referred to as flash) that can occur at the mold parting line. The mold parting line is the centerline of a part that is uniform on both sides of it. The full metallurgical report is included in the docket.
a loss of engine power due to the fatigue fracture of the number 7 cylinder exhaust rocker arm as a result of a grinding operation during manufacture.
Source: NTSB Aviation Accident Database
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