# NTSB CHI07LA173: Air Tractor AT-301, N23667, Fergus Falls, MN, June 20, 2007 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: June 20, 2007, 08:00 local (13:00 UTC) - Place: Fergus Falls, MN - Coordinates: 46.279396, -96.05931 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.2794&lon=-96.0593&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report March 31, 2008 - Report: Approved by Office Director - Parties: FAA - Minneapolis FSDO - NTSB case key (mKey): 66095 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI07LA173 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/66095/pdf - Page: https://openairdocs.org/ntsb/CHI07LA173 ## Probable cause The propeller blade failure during climb due to a fatigue crack. The oil leak that obstructed the pilot's vision was a factor in the accident. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, climb - to cruise - propeller system/accessories,blade - failure (cause) - propeller system/accessories,blade - fatigue (cause) - Forced landing, emergency descent/landing - Hard landing, emergency landing - landing gear,main gear - separation - landing gear,main gear - overload - fluid,oil - leak (contributing factor) - window,flight compartment window/windshield - obstructed (contributing factor) - Nose over, emergency landing - terrain condition - ground ## Analysis The agricultural spray airplane sustained substantial damage during a forced landing following a severe engine vibration during cruise flight. The pilot reported that he was in cruise flight about 500 feet above ground level (agl) when the engine and airframe started to vibrate violently, and the windshield became covered with oil. He made a forced landing to a field, but the main landing gear broke off and the airplane flipped over. Inspection of the airplane revealed that one of the propeller blades was missing about 9 inches of the propeller blade tip. The propeller blade was cut and the piece with the fracture surface was sent to the National Transportation Safety Board's Materials Laboratory for examination. The inspection of the fracture surface revealed that the propeller bladed failed as a result of a fatigue crack, with features typical of impact of a rotating propeller blade with a foreign object. Aircraft maintenance records indicated that the propeller blade was repaired and overhauled on October 21, 2003. The overhaul documents indicated that the no discrepancies were found when the propeller blades and hub underwent visual and non-destructive testing. The aircraft operator reported that he had purchased the propeller blade from another operator as a "0" time blade since major overhaul. Since installing the propeller on the accident airplane, it had been flown for about 30 hours. The operator reported that the accident airplane did not have a propeller strike during the 30 hours of operation prior to the accident flight. ## Factual narrative On June 20, 2007, at approximately 0800 central daylight time, an Air Tractor AT-301, N23667, sustained substantial damage during a forced landing following a severe engine vibration during cruise flight near Fergus Falls, Minnesota. The 14 Code of Federal Regulations Part 137 flight departed Fergus Falls Municipal Airport-Einar Mickelson Field (FFM), Fergus Falls, Minnesota, at approximately 0750 for a local aerial application flight. The commercial pilot reported minor injuries. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed. The pilot reported that he was in cruise flight about 500 feet above ground level (agl) when the engine and airframe started to vibrate violently. The windshield became covered with fluid, and because the door had come open, fluid was getting into the cockpit making it difficult for the pilot to see. He executed a forced landing to a field. The main landing gear broke off and the airplane flipped over. The pilot released his harness and evacuated the airplane. The inspection of the airplane revealed that one of the propeller blades was missing about nine inches of the propeller blade tip. The propeller blade was cut and the piece with the fracture surface was sent to the National Transportation Safety Board's (NTSB) Materials Laboratory for examination. The inspection of the fracture surface revealed that the central and leading edge portions of the fracture face were relatively flat and perpendicular to the exterior surfaces of the blade, gross features normally associated with fatigue. The trailing edge portion of the fracture was on a slant plane and displayed a grainy surface texture, consistent with a final overstress fracture region. The central portion of the fracture displayed an impacted surface consistent with intermittent contact with its mating fracture face; another gross feature consistent with fatigue. The inspection revealed a black indentation on the flat surface of the blade and that the crack arrest marks would be indicative of a crack originating in that vicinity. The indentation was oriented chordwise and penetrated progressively deeper into the surface toward the trailing edge, features typical of impact of a rotating propeller blade with a foreign object. Aircraft maintenance records indicated that the Hamilton Standard propeller, model 22D40, type 6533A-12, was repaired and overhauled on October 21, 2003. The overhaul documents indicated that no discrepancies were found when the propeller blades and hub underwent visual and non-destructive testing. The propeller hub was checked using magnaflux and eddy current non-destructive testing procedures. The propeller blades were checked using the zyglo non-destructive testing procedure. The aircraft operator reported that he had purchased the propeller blade in the winter of 2005/2006, and that the propeller was installed on the airplane in the spring of 2006. The propeller was purchased from another operator as a "0" time blade since major overhaul (SMOH). The operator reported that the propeller blade appeared to be "freshly overhauled" and it looked fine to him. Since installing the propeller on the accident airplane, it had been flown for a total of about 30 hours. The accident airplane was used as a backup airplane, so it did not fly regularly. The operator reported that the accident airplane did not have a propeller strike with a foreign object during the 30 hours of operation prior to the accident flight. ## Aircraft - Registration: [N23667](https://openairdocs.org/deregistered/N23667-2017-03-27), registration cancelled 2017-03-27, S/N 301-0410, built 1981 (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: 301-0410 - Airframe hours: 5981 - Engines: Pratt & Whitney R-1340 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: West Central Aerial Sprayers Inc - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, June 1, 2007 - Departed: FFM, FERGUS FALLS, MN - Airport: FFM, Fergus Falls Muni-Einar Mickel ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; injuries: minor; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2; seat: center; flight hours: 3,501 total, 300 in this make and model, 3,393 as pilot in command, 65 in the last 90 days, 65 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 260° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 66 °F, dew point 57 °F - Altimeter: 30.03 inHg - Observed at: KFFM, 4 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 20070620014719A](https://openairdocs.org/incident/20070620014719A), Jun 20, 2007: Airtrc AT301, Fergus Falls, MN, Destroyed. (-23) While in cruise flight at approximately 1500 AGL, the aircraft started to vibrate violently. The propeller speed ring came off (aircraft area encasing… 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.