# NTSB WPR19LA255: Sikorsky S58, N1168U, Azusa, CA, September 11, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: September 11, 2019, 13:00 local (20:00 UTC) - Place: Azusa, CA - Coordinates: 34.123889, -117.898612 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=34.1239&lon=-117.8986&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: RAL FSDO - NTSB case key (mKey): 100235 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR19LA255 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/100235/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=100235 - Page: https://openairdocs.org/ntsb/WPR19LA255 ## Probable cause The in-flight separation of a section of the tail rotor blade due to a fatigue crack, which resulted in the pilot’s forced autorotation into a field. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor: tail rotor blade](https://openairdocs.org/ntsb-findings/01046410): Aircraft › Aircraft propeller/rotor · Fatigue/wear/corrosion (probable cause); cases with it: [Sikorsky S-58ET, 1 case](https://openairdocs.org/ntsb-findings/01046410/cases.md?model=8141803), [All aircraft, 31 cases](https://openairdocs.org/ntsb-findings/01046410/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) (defining event); cases with it: [Sikorsky S-58ET, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=8141803), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Enroute: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Sikorsky S-58ET, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=8141803), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot was conducting a ferry flight. During cruise flight while at an altitude of about 1,000 ft above ground level and at an airspeed of about 110 knots, one of the helicopter’s tail rotor blades separated, which resulted in a partial separation of the remaining tail rotor assembly and a forced autorotation. The remaining tail rotor assembly subsequently impacted the vertical stabilizer. The mechanic who performed the daily inspection of the helicopter before the accident flight did not observe any evidence of a crack on the tail rotor blades. The separated section of the tail rotor blade was not recovered. Postaccident fractographic examination of the tail rotor blade piece containing the root end revealed that most of the blade had cracked due to fatigue. No nicks, gouges, damage, or contamination were observed. Further examination revealed that the blade met the design specifications of the engineer drawings. Maintenance records revealed that the rotor blade was most recently repaired in April 2007, but details of the repair work were not available. ## Factual narrative A review of the maintenance records revealed that, on April 20, 2007, the blade that had separated from the tail rotor assembly was repaired. According to documents, details of the repairs were on file at the repair station that performed the work. The maintenance records also indicated that the paint on the blade was removed and that the blade was refinished and static balanced. After completion of the work, the blade was deemed to be in an airworthy condition. The company that performed the last repair stated that it retained no documents related to the work performed on the blade and could provide no additional information. The tail rotor blade was installed on the accident helicopter on May 13, 2013, when the helicopter had accumulated a total time of 18,897 hours. The blade had a total time of 885 hours and an “on condition” retirement life and was in compliance with all applicable airworthiness directives and service bulletins. According to the mechanic who performed the daily inspection of the helicopter on the morning of the accident flight, he wiped down the tail rotor blades and saw no working metal, cracks in the paint, or evidence of a crack. On September 11, 2019, about 1300 Pacific daylight time, a Sikorsky S-58ET helicopter, N1168U, was substantially damaged when it was involved in an accident near Azusa, California. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 ferry flight. The pilot reported that he was ferrying the helicopter from Shafter Airport-Minter Field (MIT), Shafter, California, to Corona Municipal Airport (AJO), Corona, California. During cruise flight, when the helicopter was about 1,000 ft above ground level and at an airspeed of about 110 knots, the pilot “heard and felt a loud bang without the onset of noise or vibration.” Subsequently, the helicopter began to yaw to the right, and the pilot conducted an immediate autorotation and landed the helicopter in a baseball field. A postflight inspection revealed that one tail rotor blade had separated from the tail rotor assembly and that the remaining three tail rotor blades, which remained attached to the tail rotor assembly, exhibited dents and chordwise bends, The 90° gearbox had fractured, exposing the internal gears, and the vertical stabilizer was impact damaged. (See figure 1.) Figure 1. Left-side view of the tail rotor assembly, 90° degree gear box, and the vertical stabilizer (Source: Pilot). The separated section of the tail rotor blade was not recovered. The shank and the other three blades of the tail rotor assembly were shipped to the National Transportation Safety Board’s Materials Laboratory for examination. Fractographic examination of the shank revealed the blade had separated perpendicularly to the blade length along a chord plane located about 3 inches from the bottom of the blade. (See figure 2.) Figure 2. Side view of tail rotor blade shank. Examination of the tail rotor shank revealed athumbnail-shaped pattern emanating from one side of the blade that was consistent with fatigue that had propagated through about three-quarters of the blade. No nicks, gouges, damage, or contamination were observed at the fatigue origin. Further examination of the tail rotor blade shank and the other three tail rotor blades revealed that they met the design specifications identified in the engineering drawings. ## Aircraft - Registration: [N1168U](https://openairdocs.org/aircraft/N1168U), registered now, S/N 58-1070, built 1958 (OpenAirDocs) - Reported make and model: Sikorsky S58 (ET) - Registry model: [Sikorsky S-58ET](https://openairdocs.org/model/sikorsky-s-58et) (registry code 8141803) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PT6T-6](https://openairdocs.org/engine/pratt-whitney-canada-pt6t-6) (registry code 52106, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 58-1070 - Year built: 1959 - Airframe hours: 19929 - Engines: Pratt & Whitney PT6T-6 970 horsepower turbo shaft; Pratt & Whitney PT6T-6 970 horsepower turbo shaft - Damage: Substantial damage - Flight: Ferry, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Continuous airworthiness, August 1, 2019 - Departed: MIT, Shafter, CA - Destination: AJO, Corona, CA - Flight plan: Company VFR - Equipment: Satellite tracking device, Handheld GPS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 49; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review May 6, 2019; seat: right; restraint: 4-point; flight hours: 9,819 total, 1,022 in this make and model, 9,700 as pilot in command, 43 in the last 90 days, 22 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 260° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 75 °F, dew point 55 °F - Altimeter: 30.00 inHg - Observed at: KPOC, 7 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 20190911012989A](https://openairdocs.org/incident/20190911012989A), Sep 11, 2019: Sikorsky S-58ET, Azusa, CA, Substantial damage. The aircraft was in level cruise at about 1000 ft. AGL with an airspeed around 110 KTS on a ferry flgith from mit to ajo. Over the city of Azusa,CA the pilot… ## Other investigations on N1168U (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 LAX89FA160](https://openairdocs.org/ntsb/LAX89FA160), Apr 15, 1989: Sikorsky S-58ET (N1168U), Santa Ana, CA, substantial damage. Probable cause: FAILURE OF THE LANDING GEAR RESULTING FROM EXCESSIVE LOADING DURING GROUND OPERATIONS, AND FATIGUE CRACKING. ## Docket (7 files) The files NTSB released with the investigation on May 25, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=100235. 12.7 MB in all. - Materials laboratory factual report (item 1, PDF, 10 pages, 5.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13312746&FileExtension=pdf&FileName=20-035%20Materials%20Lab%20-%20Factual%20Report%20(WPR19LA255)_revised_30AUG2021-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 9 pages, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13132234&FileExtension=pdf&FileName=6120_1%20for%20N1168U%209-11-19_Redacted-Rel.pdf - Pilot's statement (item 3, PDF, 1 page, 476 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13132794&FileExtension=pdf&FileName=Tim%20West%20Statement%20of%20Events_Redacted-Rel.pdf - Memo for record damage summary (item 4, PDF, 2 pages, 328 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13309426&FileExtension=pdf&FileName=Memo%20for%20Record%20WPR19LA255%20Damage%20Summary-Rel.pdf - Memo for record (email summaries) (item 5, PDF, 1 page, 141 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13310612&FileExtension=pdf&FileName=Memo%20for%20Record%20WPR19LA255%20Email%20Summaries%20-Rel.pdf - Memo for record (maintenance records) (item 6, PDF, 4 pages, 785 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13317810&FileExtension=pdf&FileName=Memo%20for%20Record%20WPR19LA255%20Maintenance%20Records-Rel.pdf - Photos (item 7, PDF, 6 pages, 3.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13310657&FileExtension=pdf&FileName=Photos%20for%20WPR19LA255-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.