VAN NUYS, CA, USA
N10HJ
Hefner Pitts S1S
The pilot departed and requested a right-hand departure to the practice area. During the downwind departure he declared an emergency and witnesses observed the aircraft spiraling downward at a 45-degree angle into a residential street. Parts from the aircraft were found some distance from the accident site. The propeller along with the severed crankshaft flange were found still bolted together less part of one propeller blade. Metallurgical examination revealed that a blade had failed midspan due to fatigue. The propeller was being operated above the design rpm red line of 2,700. Additionally, the propeller was being subjected to gyroscopic aerobatic loads. An rpm restriction for the propeller mandated by an airworthiness directive was not placarded on the instrument panel per the AD. The engine was designed for a type certificated helicopter application and was approved for a 3,200 rpm red line.
HISTORY OF FLIGHT On August 17, 1997, at 1300 hours Pacific daylight time, an experimental Hefner-Pitts, S1S, N10HJ, was destroyed during a forced landing at Van Nuys, California. The pilot received fatal injuries. Visual meteorological conditions prevailed for the personal flight, and no flight plan was filed nor required. The flight departed from runway 16R at the Van Nuys airport. The pilot requested a right-hand downwind departure to a practice area. About 1.5 miles northwest of the airport the pilot declared a "mayday" three times. Tower personnel observed the aircraft spiraling downward. Ground witnesses stated that the aircraft descended at a 45-degree angle into the four-lane residential area street. A path of wreckage debris paralleled the east-west street over a distance of 281 feet. PERSONNEL INFORMATION The private pilot was rated for single engine land airplanes. According to the pilot's logbook, at the time of the accident he had accumulated about 37 hours in the accident airplane. AIRCRAFT INFORMATION According to the logbook records, the airplane was amateur built January 7, 1988. The last inspection was documented as an annual inspection dated March 26, 1997. At that time, 410.4 hours were listed as the tachometer time. At the time of the accident the tachometer indicated 494.88 hours. The Lycoming HIO-360-D1A, engine was designed for helicopter applications. It is rated at 190 hp at 3,200 rpm. The Sensenich 76EM8 series propeller is designed to operate at a maximum of 2,700 rpm. The propeller also has a requirement for an instrument panel placard to disallow continuous operation between 2,150 and 2,350 rpm (AD 84-13-05) which was not installed on the panel. The accident airplane tachometer was placarded/marked with a red line at 3,250 rpm, a yellow arc from 3,000 to 3,225 rpm, and a green arc from 1,950 to 3,000 rpm. WRECKAGE AND IMPACT INFORMATION The airplane collided at the center turn lane of a four-lane residential area street. The initial heading of the aircraft was about 090 degrees. The wreckage path was measured to be about 281 feet long. At the initial point of impact both wheel/tire imprints were near symmetrically transferred onto the asphalt. The engine assembly impacted the asphalt leaving a continuous trail of oil to the point of rest. The propeller was located on the north side of the street on private property. The propeller was found with the severed crankshaft flange attached and missing a section of one blade. The severed section of the propeller blade was not recovered. The fuel tank was found ruptured and empty with fuel spillage noted at the initial point of impact and beyond. The cowling and engine accessory parts were found in a residential area about 2,500 feet northwest of the accident site. During the accident site examination of the propeller there were two of the six propeller mounting bolts found safety wired. TESTING AND RESEARCH The propeller with the severed crankshaft flange bolted together were sent to the Safety Board Materials Laboratory for examination and analysis. During laboratory examination of the bolts the torque was measured to vary from 25 to 40 foot-pounds. According to the laboratory report, the propeller blade and the crankshaft flange revealed evidence of fatigue cracking. The fatigue origin area for the blade fatigue crack was located at a small preexisting depression in the blade's convex surface about 2.3 inches from the leading edge. The crankshaft flange was measured and was 0.381 inches thick. This thickness is below the specified 0.440-inch nominal thickness of the newer flange. For more detailed information, please refer to the Metallurgist Factual Report. MEDICAL AND PATHOLOGICAL INFORMATION On August 18, 1997, the Los Angeles County Medical Examiner performed an autopsy on the pilot. During the course of the autopsy samples were obtained for toxicological analysis by the FAA Civil Aeromedical Institute in Oklahoma City, Oklahoma. The results of the analysis were negative for carbon monoxide, cyanide, volatiles, and drugs. ADDITIONAL INFORMATION The wreckage was released to the insurance company representative on February 3, 1998.
the operation of the propeller beyond the design rpm limitations and the resultant gyroscopic loads from aerobatics. Contributing to the accident was the lack of a required instrument panel rpm restriction for the propeller mandated by an airworthiness directive.
Source: NTSB Aviation Accident Database
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