# NTSB CEN19LA156: Rockwell S 2R, N4907X, Oakes, ND, May 25, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: May 25, 2019, 14:30 local (19:30 UTC) - Place: Oakes, ND - Coordinates: 46.096942, -97.919441 - Nearby events: https://openairdocs.org/map.md?lat=46.0969&lon=-97.9194&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA FSDO, Honeywell - NTSB case key (mKey): 99496 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN19LA156 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99496/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99496 - Page: https://openairdocs.org/ntsb/CEN19LA156 ## Probable cause The failure of the helical cam gear of the engine assembly due to fatigue cracks in the gear teeth, which resulted in a total loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Accessory gear-boxes](https://openairdocs.org/ntsb-findings/01058300): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Rockwell International S-2R, 1 case](https://openairdocs.org/ntsb-findings/01058300/cases.md?model=7630202), [All aircraft, 19 cases](https://openairdocs.org/ntsb-findings/01058300/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 (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Rockwell International S-2R, 8 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=7630202), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) ## Analysis The pilot was conducting an agricultural application flight in the turbopropeller-equipped airplane when the engine lost total power. The pilot maneuvered the airplane for a forced landing to an uneven field, resulting in substantial damage to the fuselage and wings. Teardown examination of the engine revealed that the teeth of the engine’s helical cam gear were fractured. Several of the gear teeth cracks showed signatures consistent with fatigue failure. The engine assembly had a relatively low time in service (485 hours) since its most recent overhaul. The helical cam gear assembly did not show pre-existing installation anomalies. The type and degree of damage to the helical cam gear was indicative of an uncoupling of the high-speed pinion from the helical cam gear of the engine torque sensor. The uncoupling event resulted in the continuous activation of the negative torque system, which likely drained the oil in the propeller and increased the propeller blade angle. This action would have resulted in an increase in engine operating temperature and subsequent loss of engine power. ## Factual narrative On May 25, 2019, about 1430 central daylight time, a Rockwell S2R-10 airplane, N4907X, sustained substantial damage when it was involved in an accident near Oakes, North Dakota. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot reported that he was spraying a field about 10 miles southeast of his home airport. After completing 15 spray runs, the pilot maneuvered the airplane for another spray run when the engine lost total power and the pilot could not maintain altitude. The pilot maneuvered the airplane for a forced landing in a field, during which the fuselage and wings were substantially damaged. The pilot exited the airplane without injuries. The engine had about 485 hours of time in service since its most recent overhaul, and about 12 hours since its most recent annual inspection. The engine was successfully operated in a test cell at idle power. After the engine run, the front section of the engine was disassembled and examined. The helical cam gear was found with its gear teeth fractured and smeared. Several of the gear teeth cracks showed fatigue signatures during metallurgical examination. The helical cam gear assembly did not show any pre-existing installation anomalies and no other pre-impact anomalies were found with the engine. ## Aircraft - Registration: [N4907X](https://openairdocs.org/deregistered/N4907X-2021-10-02), registration cancelled 2021-10-02, S/N 2099R, built 1974 (OpenAirDocs) - Reported make and model: Rockwell S 2R (No Series) - Registry model: [Rockwell International S-2R](https://openairdocs.org/model/rockwell-international-s-2r) (registry code 7630202) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 2099R - Year built: 1974 - Airframe hours: 12813 - Engines: Honeywell TPE-331-10 940 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Bearcreek Flying Service LLC - Registered owner: Plath Aviation - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 21, 2019 - Departed: 2D5, Oakes, ND - Destination: 2D5, Oakes, ND - Equipment: Satellite tracking device ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 39; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review April 15, 2018; seat: center; restraint: 5-point; flight hours: 8,620 total, 3,950 in this make and model, 8,606 as pilot in command, 12 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 79 °F ## 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 20190525005299A](https://openairdocs.org/incident/20190525005299A), May 25, 2019: Rockwell International S-2R, Oakes, ND, Substantial damage. N4907X departed 2D5 at 2 pm headed to the south east about 10 na miles from the airport. Pilot started spraying on the east side of the field spraying north… ## Other investigations on N4907X (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 FTW96LA275](https://openairdocs.org/ntsb/FTW96LA275), Jun 24, 1996: Rockwell S2R (N4907X), Las Animas, CO, substantial damage. Probable cause: inadequate preflight planning/preparation by the pilot. Factors relating to the accident were: the unfavorable wind condition for takeoff, and the terrain condition beyond the end of the runway. ## Docket (3 files) The files NTSB released with the investigation on February 16, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99496. 7.0 MB in all. - NTSB form 6120 pilot operator report CEN19LA156 (item 1, PDF, 9 pages, 5.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13208917&FileExtension=pdf&FileName=NTSB%20Form%206120%20Pilot%20Operator%20Report%20CEN19LA156_Redacted-Rel.pdf - Memorandum for the record engine examination findings CEN19LA156 (item 2, PDF, 3 pages, 558 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13207389&FileExtension=pdf&FileName=Memorandum%20for%20the%20Record%20Engine%20Examination%20Findings%20CEN19LA156_Redacted-Rel.pdf - Photo array CEN19LA156 (item 3, PDF, 2 pages, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13207499&FileExtension=pdf&FileName=Photo%20Array%20CEN19LA156-Rel.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.