# NTSB LAX02LA257: Air Tractor AT-301, N8793S, Dos Palos, CA, August 22, 2002 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 22, 2002, 07:30 local (14:30 UTC) - Place: Dos Palos, CA - Coordinates: 36.962223, -120.629997 - Nearby events: https://openairdocs.org/map.md?lat=36.9622&lon=-120.6300&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report December 28, 2004 - Report: Approved by Office Director - Parties: Federal Aviation Administration - ADs cited in the narratives: [AD 81-13-06 R2](https://openairdocs.org/ad/81-13-06-R2) (OpenAirDocs) - NTSB case key (mKey): 55548 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX02LA257 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/55548/pdf - Page: https://openairdocs.org/ntsb/LAX02LA257 ## Probable cause the failure of the propeller blade due to fatigue. Factors in the accident were the inadequate maintenance-repair of the blade, and, inadequate pilot preflight inspections. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - normal - propeller system/accessories,blade - fatigue (cause) - maintenance,inspection - inadequate, other maintenance personnel (contributing factor) - propeller system/accessories,blade - separation (cause) - aircraft preflight - inadequate, pilot in command (contributing factor) - Forced landing, emergency descent/landing - Nose over, landing - roll - terrain condition - soft - terrain condition - open field ## Analysis During cruise flight the engine started to vibrate and the pilot made a forced landing in a newly plowed field and the airplane nosed over after encountering soft soil. The pilot had been crop dusting for about 7.5 hours when the event occurred. The outboard portion of one of the propeller blades had separated. A review of the airframe records indicated that the propeller was overhauled about 10 months prior to the accident. A metallurgical examination of the failed blade revealed it had failed as a result of fatigue cracking that originated from a nick, located on the flat side of the blade's leading edge. Also observed were groove marks that were relatively uniform and consistent with tool marks left by a file. In accordance with the overhaul manual, a field repair can be done to grind or file out corrosion of the blade, with a dye penetrant inspection to detect any visible damage or cracks (Hamilton Standard 130B Blade Overhaul Manual). The overhaul manual notes that tool and file marks should be polished out as one of the final steps in the process. According to the FAA approved flight manual, during the preflight walk-around inspection, the pilot is to inspect the propeller blades for nicks and cracks. ## Factual narrative On August 22, 2002, at 0730 Pacific daylight time, an Air Tractor AT-301 restricted category airplane, N8793S, came to rest inverted in a newly disked open field during a forced landing that was precipitated by a loss of a propeller blade while in cruise flight. The airplane, operated by Spain Air under the provisions of 14 CFR Part 137 as a aerial application operation, sustained substantial damage. The commercial pilot, the sole occupant, was not injured. Visual metrological conditions prevailed for the local area flight and no flight plan had been filed. The flight departed a private airstrip about 0650. According to the pilot, he had been crop dusting since midnight. There were no mechanical anomalies noted during any of the flights. On the accident flight part of the propeller blade came off. The pilot stated that the engine started to vibrate and he made an emergency landing in a cotton field. On the landing rollout the landing gear caught on the soft dirt and the airplane nosed over, coming to rest inverted. AIRCRAFT INFORMATION Airframe records indicated that the propeller had been overhauled on October 31, 2001. During the overhaul, the propeller blades, manufactured by Pacific Propeller, Kent, Washington, were converted to the Hydromatic Blade 6533A-12. The overhaul records show that the customer supplied the hub assembly, and that there was pitting on the blade shanks and bearings. According to Pacific Propeller the appropriate inspection document for the propeller blades is the Hamilton Standard 130B Blade Overhaul Manual. The manual contains information for a dye penetrant inspection to detect cracks or other discontinuities in damaged areas, as well as dimensional checks for dressing out the propeller blade during overhaul. The manual has a section that deals with a local (field) repair to grind or file corrosion out of the blade. Once the grinding is complete a dye penetrant inspection should be done to detect any damage. Airworthiness Directive 81-13-06 R2 (Amendment 39-4133, revised by Amendment 39- 4409, and further revised by Amendment 39-6271) applies to Hamilton Standard propeller blades and was issued to prevent propeller blade failure due to corrosion and fatigue. The AD calls for an inspection of the propeller blades to be accomplished within 90 days after July 1, 1982, or within 18 months since the last inspection. If corrosion is found the propeller blades are required to be reinspected at intervals not to exceed 18 months since the last inspection. The 18 month interval can be extended up to 60 months if no corrosion is found. According to the manufacturer's Federal Aviation Administration approved airplane flight manual preflight visual walk-around inspection, the pilot is to inspect the "prop blades for nicks or cracks." The propeller blade was examined by the Safety Board Metallurgical Laboratory in Washington, D.C. The blade had a chordwise fracture about 40 inches from the butt end. The blade fracture surface displayed shiny, faceted fracture features that spanned 60 percent of the chord's width. This region had crack arrest marks and a smoothly curving boundary, features consistent with fatigue. The fatigue features emanated from multiple origins from a nick on the flat side of the blade's leading edge. The nick measured 0.2 inch wide chordwise, 0.15 inch spanwise and 0.06 inch deep. Adjacent to the nick were several straight, parallel grooves. The grooves were uniform, and consistent with tool marks. ## Aircraft - Registration: [N8793S](https://openairdocs.org/deregistered/N8793S-2008-02-13), registration cancelled 2008-02-13, S/N 301-0195, built 1979 (OpenAirDocs) - Reported make and model: Air Tractor AT-301 - Registry model: [Air Tractor AT-301](https://openairdocs.org/model/air-tractor-at-301) (registry code 0390103) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: AT 301-0195 - Airframe hours: 13904 - Engines: Pratt & Whitney R1340 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: Spain Air - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, August 8, 2002 - Departed: PVT, DOS PALOS, CA - Destination: PVT, DOS PALOS, CA - Airport: 28CA, Dos Palos Airport, runway 290, 2,600 × 60 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 48; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; last flight review November 15, 2001; seat: center; flight hours: 18,542 total, 16,000 in this make and model, 18,542 as pilot in command, 300 in the last 90 days, 125 in the last 30 days, 6 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 310° at 4 knots - Visibility: 3 statute miles - Lowest ceiling: none - Temperature: 54 °F, dew point 50 °F - Altimeter: 29.95 inHg - Observed at: MCE, 19 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 20020822021999A](https://openairdocs.org/incident/20020822021999A), Aug 22, 2002: Airtrc AT301, Dospalos, CA, Substantial damage. (-23) One propeller blade failed/loss of a portion of the blade. Engine vibration caused failure of the engine mount. The p&w R1340 engine separated from the… ## Other investigations on N8793S (1) 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. - [NTSB LAX82DA046](https://openairdocs.org/ntsb/LAX82DA046), Jan 21, 1982: Air Tractor 301 (N8793S), Dos Palos, CA, substantial damage 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.