# NTSB DEN07LA138: Air Tractor AT-301, N69WN, Alamosa, CO, August 18, 2007 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: August 18, 2007, 07:52 local (13:52 UTC) - Place: Alamosa, CO - Coordinates: 37.435001, -105.866668 - Nearby events: https://openairdocs.org/map.md?lat=37.4350&lon=-105.8667&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report January 31, 2008 - Report: Approved by Office Director - Parties: FAA Flight Standards District Office - NTSB case key (mKey): 66480 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN07LA138 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/66480/pdf - Page: https://openairdocs.org/ntsb/DEN07LA138 ## Probable cause The failure of the number one cylinder due to fatigue. Contributing to the accident was the pilot's diminished visual lookout due to the oil covered windscreen. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - mech failure/malf, maneuvering - aerial application - engine assembly,cylinder - fatigue (cause) - engine assembly,cylinder - failure,total (cause) - Forced landing, descent - emergency - On ground/water encounter with terrain/water, emergency landing - visual lookout - diminished, pilot in command (contributing factor) - terrain condition - dirt bank/rising embankment ## Analysis The airplane was conducting aerial applications of anti-sprouting chemicals when the number one cylinder head separated. The windscreen was covered in oil, obscuring the pilot's view. The pilot dropped his chemical load and performed a forced landing to a dirt road. During the landing, the left wing impacted a sand berm and the airplane nosed over, coming to rest inverted, and resulting in substantial damage. The pilot reported no additional anomalies with the airplane's systems. Examination of the fracture surface revealed fatigue cracking initiated from multiple locations in a root of the head threads and propagated in an arc to the outer surface of the combustion chamber wall. ## Factual narrative On August 18, 2007, at 0752 mountain daylight time, an Air Tractor AT-301, N69WN, operated by Rocky Mountain Ag, Inc., was substantially damaged during a forced landing near Alamosa, Colorado. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 137 without a flight plan. The commercial pilot sustained minor injuries. The local flight departed Monte Vista Municipal Airport (MVI), approximately 0730. According to the owner of Rocky Mountain Ag, Inc., the airplane was carrying a load of MH-30, an anti-sprouting chemical, when the number one cylinder head separated. as a result, the windscreen was covered in oil, obscuring the pilot's view. The pilot dropped his chemical load and performed a forced landing on a dirt road. During the landing, the left wing impacted a sand berm and the airplane nosed over. The outboard three feet of the left wing was separated, the rudder and vertical stabilizer were crushed down, and the skid plate on the fuselage canopy separated and came aft into the cabin. Aside from the separation of the number one cylinder, the pilot reported no additional anomalies with the airplane's systems. The number one cylinder was sent to the National Transportation Safety Board's Materials Laboratory in Washington, D.C., for further examination. Examination of the fracture face revealed a rough grainy surface typical of overstress, with the exception of an area between the intake and exhaust ports. The area between the ports displayed a smoother surface that was oriented perpendicular to the cylinder wall, typical of fatigue cracking, and covered with a black deposit consistent with combustion products. Combustion products were also evident on the adjacent cooling fin surface and oriented radially outwards. Closer examination of the fracture face revealed that the fatigue cracking initiated from multiple locations in a root of the head threads and propagated in an arc to the outer surface of the combustion chamber wall. The fatigue zone contained shallow depressions consistent with the presence of porosity in the cylinder head material. According to the engine maintenance records, the number one cylinder, part number R 1340 (223), was overhauled on June 22, 2005, by Aircraft Cylinders of America, Inc. The last 100-hour inspection was performed on the engine on April 24, 2007. In addition, the number three cylinder was removed and replaced due to a "blown head" on July 18, 2007. Following this accident, Air Tractor revised their service letter #97 "Cockpit Overturn Skid Plate" to incorporate a "new wider clamp" and larger attaching bolts to "strengthen both the front and rear connections to the airplane frame structure." ## Aircraft - Registration: [N69WN](https://openairdocs.org/aircraft/N69WN), registered now, S/N 301-0683, built 1988 (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: 301-0683 - Airframe hours: 5109 - Engines: Pratt & Whitney R-1340 ANI 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: Rocky Mountain Ag Inc - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 1, 2007 - Departed: MVI, MONTE VISTA, CO - Destination: MVI, Monte Vista, CO ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; injuries: minor; commercial, airline transport, flight instructor; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review May 1, 2007; seat: single; flight hours: 4,000 total, 1,000 in this make and model, 3,950 as pilot in command, 130 in the last 90 days, 60 in the last 30 days, 6 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 57 °F, dew point 48 °F - Altimeter: 30.29 inHg - Observed at: ALS ## 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 20070818016379A](https://openairdocs.org/incident/20070818016379A), Aug 18, 2007: Airtrc AT301, Alamosa, CO, Substantial damage. (-23) Aircraft lost #1 cylinder barrel head, spewed oil on windscreen. Pilot made a forced landing (county rd. 104), hit a sand berm and nosed over. Aircraft… 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.