# NTSB LAX98LA258: M. C. Thomas Stewart S-51, N151MT, Jackson, CA, August 5, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 5, 1998, 10:20 local (17:20 UTC) - Place: Jackson, CA - Coordinates: 38.349365, -120.770462 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=38.3494&lon=-120.7705&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report June 22, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 43685 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX98LA258 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43685/pdf - Page: https://openairdocs.org/ntsb/LAX98LA258 ## Probable cause Failure of the propeller governor pulley drive shaft due to a modification made to the system by the owner that included welding a retaining pin to the center of the heat treated drive shaft, which compromised the shaft's design strength margin. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, cruise - normal - propeller system/accessories,governor - failure,total (cause) - maintenance,modification - improper, owner/builder (cause) - Forced landing, emergency descent/landing - On ground/water collision with object, landing - roll - object - pole - object - tree(s) ## Analysis While en route to the destination airport, the airplane experienced a loss of engine power. The pilot made a forced landing on a highway and collided with a snow pole. The airplane veered off of the road and came to rest after it collided with a tree. The owner/builder stated that he had modified the drive shaft from the original 'V' belt drive to a dual 'serpentine' belt/pulley system. He further stated that in order to install the new belt/pulley system, he had to weld a retaining pin in the center of the original drive shaft. The propeller governor pulley was found at the bottom of the engine compartment and the shaft was found to have separated at the center point. The drive shaft exhibited a bluing and discoloration at the center where the owner had welded it on the pin. It was noted that the original manufacturer of the propeller governor drive shaft had placed a heat treat stamp on the shaft. ## Factual narrative On August 5, 1998, at 1020 hours Pacific daylight time, an experimental Stewart S-51 airplane, N151MT, experienced a loss of engine power approximately 20 miles northeast of Jackson, California. The aircraft, operated by the pilot under 14 CFR Part 91, sustained substantial damage in the ensuing forced landing on Highway 88. The private pilot was not injured. Visual meteorological conditions existed for the flight that departed the Reno, Nevada, airport at 0945. The flight was scheduled to terminate at the San Luis Obispo, California, airport. No flight plan was filed. The pilot stated that 20 minutes into the flight he noted a loss of oil and fuel pressure. The failure occurred at 5,500 feet above ground level (agl) and the nearest airport was in excess of 20 nmi away. He stated that he chose an unoccupied road to make the emergency landing. After touchdown, the airplane collided with a snow pole and veered off of the road and came to rest after colliding with a tree. The Federal Aviation Administration interviewed the owner/builder of the kit. The engine is a General Motors 502-cubic-inch displacement automotive powerplant, which was modified for installation in the airframe. The engine accessories are driven by a "V" belt system. The owner stated that he modified the drive shaft from the original "V" belt drive to a dual "serpentine" belt/pulley system. He further stated that in order to install the new system, he had to weld the new serpentine drive to the original drive shaft. He installed and welded a retaining pin on the center of the drive shaft. An examination of the airplane was conducted by a FAA inspector. He found the propeller governor pulley at the bottom of the engine compartment, with the drive shaft broken at midpoint where the retaining pin had been welded. The inspector noted a bluing and discoloration of the shaft. He further noted that the original manufacturer had placed a heat treat stamp on the shaft and the integrity of the shaft may have been compromised by the owner/builder's welding of the shaft. ## Aircraft - Registration: [N151MT](https://openairdocs.org/deregistered/N151MT-1998-09-25), registration cancelled 1998-09-25, S/N 125 (OpenAirDocs) - Reported make and model: M. C. Thomas STEWART S-51 (STEWART S-) - Registry model: [M C Thomas Const STEWART S-51](https://openairdocs.org/model/m-c-thomas-const-stewart-s-51) (registry code 05605Q4) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: S-51D - Airframe hours: 62 - Engines: GM 502 600 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Michael W. Clipperton - Registered owner: M.C. Thomas Contstruction Co. - Airworthiness certificate: Special, Experimental (Special) - Departed: RNO, RENO, NV - Destination: SBP, SAN LUIS OBISPO, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 24; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, valid medical--no waivers/lim.; seat: front; flight hours: 335 total, 26 in this make and model, 306 as pilot in command, 49 in the last 90 days, 29 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 40 statute miles - Lowest ceiling: none - Temperature: 75 °F, dew point 30 °F - Altimeter: 30.00 inHg - Observed at: TVL, 98 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19980805019749A](https://openairdocs.org/incident/19980805019749A), Aug 5, 1998: Amtr STEWARTS51, Jackson, CA, Substantial damage. Acft experienced engine failure, lost all power and made an emergency landing on highway 88, on landing, the acft ran off the highway and struck a tree. (.4)… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.