CHANDLER, AZ, USA
N791S
STAUDACHER 300S
The pilot had completed a practice acrobatic sequence when she said she heard the engine begin to 'lug.' She noted the engine oil pressure gauge was reading between 20 to 40 psi with the aircraft at full power, then almost immediately dropped to zero. The pilot selected an area for a forced landing, but as she neared the ground she said the area did not look as flat as it had initially. The pilot said that since the aircraft continued to lose power, she was committed to land. During the landing roll, the aircraft struck a berm damaging the landing gear, wings, and propeller. An internal examination of the crankcase revealed that the No. 5 connecting rod bearing had failed, although the connecting rod still remained attached to the crankshaft. The data plate indicated that the engine installed is rated for 290 hp at 2,575 rpm's. The aircraft's mechanic reported that the engine rpm was set for 2,700 rpm's.
On May 27, 1994, at 1730 mountain standard time, a homebuilt experimental Staudacher 300S, N791S, sustained substantial damage during an off-airfield forced landing 10 miles south of Chandler, Arizona. The aircraft was owned and operated by the pilot and was on a solo acrobatic practice flight. Visual meteorological conditions were prevalent at the time and no flight plan had been filed. The certificated commercial pilot sustained serious injuries. The flight originated from the Chandler Municipal airport at 1715 on the day of the accident. The pilot had completed a practice acrobatic sequence terminating between 700 and 800 feet agl, and had just begun a climb when she said she heard the engine begin to "lug." She stated that as she looked at the engine oil pressure gauge, she noted that it was reading between 20 to 40 psi with the aircraft at full power. She further stated that, as she looked, the oil pressure reading almost immediately dropped to zero. She radioed the problem to her acrobatic coach who had been observing the practice from the ground. He asked her if she thought she could return to the airport, but she replied that she would be forced to land because the aircraft was losing power. He then advised her to tighten her shoulder harness in preparation for a forced landing. The pilot said she did not immediately see a suitable forced landing area and began a search during a 180-degree left turn. The pilot selected a landing site and set up an approach. She said that as she neared the ground the terrain did not look as flat as it had initially, but since the aircraft continued to lose power, she was committed to land. During the landing roll, the aircraft struck a berm damaging the landing gear, wings, and propeller. The pilot sustained a fractured right ankle during the forced landing. A postaccident inspection of the engine was conducted. When the propeller governor was removed from the crankcase, oil was observed leaking from the two top bolt holes. A visual inspection of the bolt holes revealed that the holes extended into the internal cavity of the case. Several small pieces of metal were found in the propeller screen governor screen. An internal examination of the crankcase revealed that the No. 5 connecting rod bearing (P/N SL-13521) had failed, although the connecting rod still remained attached to the crankshaft. Further examination also revealed a smearing of the No. 3 main bearing halves. The data plate indicated that the IO-540 engine develops 290 hp at 2,575 rpm's. The aircraft mechanic reported that the engine rpm was set for 2,700 rpm's.
THE OPERATION OF THE ENGINE AT AN RPM SETTING THAT EXCEEDED THE ORIGINAL DESIGN SPECIFICATIONS AND RESULTED IN THE FAILURE OF THE NO. 5 CONNECTING ROD BEARING.
Source: NTSB Aviation Accident Database
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