# NTSB WPR17LA174: Rockwell International S 2R, N4913X, Brawley, CA, August 1, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 1, 2017, 06:55 local (13:55 UTC) - Place: Brawley, CA - Coordinates: 33.033611, -115.453056 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.0336&lon=-115.4531&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 9, 2019 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: San Diego Flight Standards - NTSB case key (mKey): 95714 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA174 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95714/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95714 - Page: https://openairdocs.org/ntsb/WPR17LA174 ## Probable cause The partial loss of engine power due to the overstress separation of three supercharger drive gear teeth. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Aircraft](https://openairdocs.org/ntsb-findings/01050000): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Rockwell International S-2R, 2 cases](https://openairdocs.org/ntsb-findings/01050000/cases.md?model=7630202), [All aircraft, 151 cases](https://openairdocs.org/ntsb-findings/01050000/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: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Rockwell International S-2R, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=7630202), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Maneuvering-low-alt flying: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Rockwell International S-2R, 7 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=7630202), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Rockwell International S-2R, 8 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=7630202), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing-landing roll: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Rockwell International S-2R, 20 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=7630202), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The commercial pilot reported that, while conducting low-level maneuvering over a field during the agricultural application flight, the engine lost partial power . The pilot leveled the wings, and the engine momentarily regained some power; however, shortly after, it started to lose power again. The pilot subsequently initiated an off-airport landing to a field. During the landing roll, the propeller struck the ground, and the landing gear were torn off. Both wings, the engine mounts, and the bottom of the fuselage sustained substantial damage. Postaccident examination of the engine revealed that three of the supercharger drive gear teeth had broken, one of which was found in the engine oil sump. Examination of the gear teeth fracture surfaces revealed features and topographies consistent with bending overstress separations. Contact patterns and pitting were noted on the pressure faces of the remaining intact gear teeth, which were indicative of heavy loading. No preexisting cracks were found. The thrust bearing exhibited damage consistent with a propeller strike. A representative from an engine overhaul facility that overhauls the accident engine make and model (but did not overhaul the accident engine) reported that it is unlikely that the gear teeth fractured during the accident sequence given that one of the separated gear teeth was found in the oil sump and not in the supercharger blower section because typically when a gear tooth separates during flight, the oil flow will carry the broken fragment down into the sump. The representative reported that the gear teeth usually break due to either a sudden engine stoppage or fatigue or stress cracking. The fatigue or stress cracking can often be the result of a propeller strike and, if left unchecked, can result in the eventual separation of the affected gear teeth. He stated that it is possible for an engine to continue operating relatively normally with only one gear tooth missing; however, multiple broken gear teeth would result in a decrease in power of the supercharger section. Maintenance records were not made available for review during the investigation; therefore, it could not be determined if a propeller strike or sudden engine stoppage was reported before the accident. ## Factual narrative On August 1, 2017, about 0655 Pacific daylight time, a Rockwell International S-2R airplane, N4913X, was substantially damaged following a partial loss of engine power and subsequent off-airport landing near Brawley, California. The commercial pilot was not injured. The airplane was registered to and operated by Farm Aviation, Inc., under the provisions of Title 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the local flight and no flight plan was filed. The flight departed from a private airstrip in Brawley at 0645. The pilot reported that he departed westbound from the private airstrip with about 180 gallons of chemical and 70 gallons of fuel on board. After climbout, he made a right turn to the east to conduct a low-level reconnaissance of the field he intended to spray. As he began to set up for the eastbound pass on the north side of the field, the engine started to lose power. The pilot leveled the wings, the engine momentarily regained some power, but started to lose power again shortly after. The pilot subsequently initiated an emergency landing to an open field. During the landing roll, the propeller struck the ground and the landing gear was torn off. Both wings, the engine mounts, and the bottom of the fuselage sustained substantial damage. On October 3, 2017, the Pratt & Whitney R1340 radial engine was examined by Federal Aviation Administration (FAA) inspectors. The inspectors reported that the engine was partially disassembled before their arrival. The inspectors reported that one of the supercharger drive gear teeth was separated and found in the engine oil sump. Further disassembly of the supercharger drive section revealed that two additional gear teeth were separated from the supercharger drive. Slight rubbing marks were observed on the supercharger impeller. The thrust bearing exhibited damage consistent after a propeller strike. The oil filter revealed signs of high carbon content and some debris with very little metallic content. Surface rust was noted on internal oil transfer tubes, the camshaft drive gear, and the supercharger drive gear. The spark plugs exhibited normal wear signatures. The inspectors further reported that the carburetor was visually inspected, and no foreign objects were observed in the venturi. The magnetos were externally examined before the gears were rotated by hand. No anomalies were found The separated supercharger gear teeth were examined at the National Transportation Safety Board Materials (NTSB) laboratory, Washington, DC. The fracture surfaces were examined using a stereomicroscope at moderate magnifications. The fractures exhibited features and topographies consistent with bending overstress separations. Contact patterns and pitting were noted on the pressure faces of the remaining intact gear teeth indicative of heavy loading. No indication of preexisting cracking was apparent. During a conversation with arepresentative from an engine overhaul facility, who commonly overhauls Pratt & Whitney R1340 radial engines, he reported that from his experience, the gear teeth most often break off due to either a sudden engine stoppage or due to fatigue or stress cracking. The fatigue or stress cracking can often be the result of a propeller strike and, if left unchecked, can result in the eventual separation of the affected gear teeth. He reported that it is possible for an engine to continue a relatively normal operation with only one gear tooth missing, however multiple broken teeth would result in a decrease in power of the supercharger section. The pilot reported that the engine had accumulated about 783 hours since overhaul, and 74 hours since the last annual inspection on November 16, 2016. No maintenance records were made available for review to determine if there was a report of a previous propeller strike or sudden engine stoppage. ## Aircraft - Registration: [N4913X](https://openairdocs.org/deregistered/N4913X-2017-08-30), registration cancelled 2017-08-30, S/N 2104R, built 1974 (OpenAirDocs) - Reported make and model: ROCKWELL INTERNATIONAL S 2R (UNDESIGNAT) - 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: 2104R - Year built: 1974 - Airframe hours: 6615 - Engines: Pratt & Whitney R-1340- AN1 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, November 16, 2016 - Departed: Brawley, CA - Destination: Brawley, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 40; injuries: none; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review April 20, 2017; seat: single; restraint: 4-point; flight hours: 2,400 total, 500 in this make and model, 2,280 as pilot in command, 60 in the last 90 days, 24 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 50° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 88 °F, dew point 73 °F - Altimeter: 29.78 inHg - Observed at: KIPL, 14 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 20170801010239A](https://openairdocs.org/incident/20170801010239A), Aug 1, 2017: Rockwell International S-2R, Brawley, CA, Substantial damage. Pilot reported while flying on the north side of the field he noticed a loss of power. He leveled the wings flying north west some power was received then… ## Other investigations on N4913X (2) 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 MKC84LA180](https://openairdocs.org/ntsb/MKC84LA180), Jun 16, 1984: Rockwell S-2R (N4913X), Pocahontas, AR, substantial damage - [NTSB FTW76DPG12](https://openairdocs.org/ntsb/FTW76DPG12), Jul 31, 1975: Aero Comdr 600S2R (N4913X), Augusta, AR, substantial damage ## Docket (6 files) The files NTSB released with the investigation on February 28, 2019, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95714. 6.6 MB in all. - NTSB Metallurgy Report (item 1, .PDF, 48 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470684&FileExtension=.PDF&FileName=NTSB%20Metallurgy%20Report-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470685&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Engine Examination (item 3, .PDF, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470686&FileExtension=.PDF&FileName=Engine%20Examination-Master.PDF - FAA Engine Report (item 4, .PDF, 61 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470687&FileExtension=.PDF&FileName=FAA%20Engine%20Report-Master.PDF - Phone Conversation with Radial Engine Expert (item 5, .PDF, 61 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470688&FileExtension=.PDF&FileName=Phone%20Conversation%20with%20Radial%20Engine%20Expert-Master.PDF - Photos (item 6, .PDF, 2 photos, 327 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40470689&FileExtension=.PDF&FileName=Photos-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.