# NTSB CEN17LA330: Air Tractor AT 401, N4532F, Pearsall, TX, August 24, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 24, 2017, 10:00 local (15:00 UTC) - Place: Pearsall, TX - Coordinates: 28.876388, -99.005279 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=28.8764&lon=-99.0053&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 13, 2020 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Federal Aviation Administration - San Antonio - ADs cited in the narratives: [AD 99-11-02](https://openairdocs.org/ad/99-11-02) (OpenAirDocs) - NTSB case key (mKey): 95898 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN17LA330 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95898/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95898 - Page: https://openairdocs.org/ntsb/CEN17LA330 ## Probable cause The fatigue crack of an engine cylinder, which resulted in a partial loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Air Tractor AT-402, 1 case](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=0390205), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-low-alt flying: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Air Tractor AT-402, 2 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=0390205), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Maneuvering-low-alt flying: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Air Tractor AT-402, 2 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=0390205), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md) - [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Air Tractor AT-402, 2 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=0390205), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Nose over/nose down](https://openairdocs.org/ntsb-events/096); cases with it: [Air Tractor AT-402, 1 case](https://openairdocs.org/ntsb-events/096/sequence.md?model=0390205), [All aircraft, 2,287 cases](https://openairdocs.org/ntsb-events/096/sequence.md) ## Analysis The commercial pilot was conducting a local, agricultural application flight when the engine experienced a partial loss of power during a spray pass. The pilot's corrective actions did not restore normal engine operation, and he conducted a forced landing to a nearby field. The airplane descended into tall vegetation and landed in soft, sandy soil and then decelerated rapidly and nosed over. Postaccident engine examination revealed a circumferential fracture of the No. 9 cylinder. Further examination determined that the cylinder fractured from a fatigue crack that had initiated at multiple locations at a valley between two cooling fins on the outside surface. The fatigue crack progressed inward and circumferentially around the cylinder before finally cracking in overstress. No discrepancies, such as corrosion pits, wear marks, or machining marks, were found at the crack initiation sites. The cylinder met the airplane manufacturer's material and hardness specifications. The fracture would have allowed combustion gasses to escape during engine operation and led to a corresponding loss of cylinder compression, which would have led to erratic engine operation and a partial loss of power. According to engine logbook documentation, no cylinder cracks were found during an airworthiness directive inspection completed about 64 flight hours before the accident. ## Factual narrative On August 24, 2017, about 1000 central daylight time, an Air Tractor AT-401, N4532F, impacted terrain during a forced landing following a partial loss of engine power near Pearsall, Texas. The commercial pilot was not injured, and the airplane was substantially damaged. The airplane was registered to and operated by Fitch's Flying Service as a Title 14 Code of Federal Regulations Part 137 without a flight plan. Day visual meteorological conditions prevailed for the local agricultural application that departed from McKinley Field Airport (T30), Pearsall, Texas, at 0900.The pilot reported that the airplane experienced a partial loss of engine power during a low-altitude spray run over a field. He noted that the engine was surging and that he was unable to regain normal engine operation. He climbed to 100 ft above ground level, jettisoned the airplane's chemical load, but the engine operation still did not improve. The pilot reported that he subsequently made a forced landing to a nearby field. The pilot stated that the airplane decelerated rapidly and nosed over when it descended into tall vegetation and landed in soft sandy soil. The vertical stabilizer and rudder were substantially damaged. A postaccident examination revealed a circumferential fracture of the No. 9 cylinder. The fractured cylinder, serial number (s/n) 4 4HN52 L215, was submitted to the National Transportation Safety Board's Materials Laboratory for additional examination. The laboratory examination revealed a large circumferential crack through the cylinder housing. The crack was located at the valley between two air cooling fins and through the forward spark plug hole. The crack measured circumferentially as 26.3 inches long, with about 5.6 inches of the remaining cylinder circumference uncracked. The widest opening of the crack was located about 8.5 inches from the bottom side of the inboard flange, and 10.5 inches from the bottom opening of the cylinder. The fracture faces exhibited features consistent with prolonged exposure to exhaust and combustion gasses for different lengths of time. Further examination revealed crack arrest and ratchet marks consistent with progressive cracking from multiple crack initiation sites. There were no discernable discrepancies, such as corrosion pits, wear marks, or machining marks present at the crack initiation sites. The crack had prorogated from the outer cylinder surfaces inward. Further examination of the crack features using a scanning electron microscope revealed fatigue striations consistent with fatigue cracking. A sample of the cylinder was tested using energy dispersive x-ray spectroscopy and x-ray fluorescence, which confirmed the material composition was consistent with an AA 200-series aluminum casting alloy. Additionally, hardness measurements were consistent with a casted AA 200-series aluminum alloy material. The engine, a Pratt & Whitney R-1340AN-1, s/n 41-12807, had accumulated 8,899.2 hours since new and 1,310.1 hourssince the last overhaul on March 5, 2009. A complete service history for the No. 9 cylinder could not be determined with the available logbook documentation. The No. 9 cylinder was not replaced or repaired during the 2009 overhaul. Based on available documentation, the No. 9 cylinder was not removed or repaired since the 2009 overhaul. According to the engine logbook, on August 1, 2017, about 64 hours before the accident, the engine cylinders were inspected in accordance with airworthiness directive No. 99-11-02 to verify that there were no visible cylinder cracks, and the corresponding logbook entry indicated "no cracks found." ## Aircraft - Registration: [N4532F](https://openairdocs.org/aircraft/N4532F), registered now, S/N 401-0769, built 1990 (OpenAirDocs) - Reported make and model: AIR TRACTOR INC AT 401 (UNDESIGNAT) - Registry model: [Air Tractor AT-402](https://openairdocs.org/model/air-tractor-at-402) (registry code 0390205) (OpenAirDocs) - Registry engine: [Pratt & Whitney PT6A-27 series](https://openairdocs.org/engine/pratt-whitney-pt6a-27-series) (registry code 52141, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 401-0769 - Year built: 1990 - Airframe hours: 6228.1 - Engines: Pratt & Whitney R-1340AN-1 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Fitch's Flying Service - Registered owner: Fitch's Flying Service - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, March 1, 2017, 264 hours before - Departed: T30, Pearsall, TX - Destination: T30, Pearsall, TX - Equipment: Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 33; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; last flight review March 10, 2017; seat: center; restraint: 4-point; flight hours: 609 total, 290 in this make and model, 545 as pilot in command, 220 in the last 90 days, 108 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: 12,000 ft broken - Temperature: 82 °F, dew point 72 °F - Altimeter: 29.92 inHg - Observed at: COT, 20 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 20170824013639A](https://openairdocs.org/incident/20170824013639A), Aug 24, 2017: Air Tractor Inc AT-401, Pearsall, TX, Substantial damage. Aircraft departed from T30 airfield in Pearsall, TX for a routine agricultural spraying application. During the flight, the aircraft lost power and made an… ## Docket (5 files) The files NTSB released with the investigation on January 3, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95898. 9.5 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 899 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479631&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Materials Laboratory Factual Report (item 2, .PDF, 6.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479632&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Engine Logbook (Excerpts) (item 3, .PDF, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479633&FileExtension=.PDF&FileName=Engine%20Logbook%20(Excerpts)-Master.PDF - Airworthiness Directive No. 99-11-02 (item 4, .PDF, 154 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479634&FileExtension=.PDF&FileName=Airworthiness%20Directive%20No.%2099-11-02-Master.PDF - Service Bulletin No. 1787 (item 5, .PDF, 256 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479635&FileExtension=.PDF&FileName=Service%20Bulletin%20No.%201787-Master.PDF 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.