# NTSB WPR22LA340: Bell Helicopter Textron 206L-1, N242BH, Banning, CA, September 10, 2022 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: September 10, 2022, 15:50 local (22:50 UTC) - Place: Banning, CA · backyard of a residence - Coordinates: 33.916332, -116.85932 - Nearby events: https://openairdocs.org/map.md?lat=33.9163&lon=-116.8593&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) - Highest injury: Minor injuries - Injuries: 3 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Cal-Fire - NTSB case key (mKey): 105896 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR22LA340 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/105896/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=105896 - Page: https://openairdocs.org/ntsb/WPR22LA340 ## Probable cause The improper attachment of the tail rotor drive shaft to the air conditioner drive pulley without a drive ring, which resulted in the failure of the hardware, a loss of tail rotor drive, and the loss of control of the helicopter followed by a hard landing and rollover. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor drive system: tail rotor drive shaft](https://openairdocs.org/ntsb-findings/01046510): Aircraft › Aircraft propeller/rotor · Incorrect service/maintenance (probable cause); cases with it: [Bell Helicopter Textron 206L-1, 1 case](https://openairdocs.org/ntsb-findings/01046510/cases.md?model=1182107), [All aircraft, 25 cases](https://openairdocs.org/ntsb-findings/01046510/cases.md) - [Maintenance](https://openairdocs.org/ntsb-findings/02062000): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell Helicopter Textron 206L-1, 1 case](https://openairdocs.org/ntsb-findings/02062000/cases.md?model=1182107), [All aircraft, 143 cases](https://openairdocs.org/ntsb-findings/02062000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) (defining event); cases with it: [Bell Helicopter Textron 206L-1, 2 cases](https://openairdocs.org/ntsb-events/333/sequence.md?model=1182107), [All aircraft, 410 cases](https://openairdocs.org/ntsb-events/333/sequence.md) ## Analysis The pilot and two passengers were returning to the base airport following an aerial firefighting mission. During the approach to the airport, the helicopter began an uncontrolled right rotation that could not be arrested despite full use of the left pedal. The pilot attempted to land in the back yard of a private residence; however, the helicopter landed hard and rolled onto its left side. The helicopter sustained substantial damage to the main rotor system, fuselage, and tailboom. An on-scene examination revealed the tail rotor drive shaft had separated at a flex coupling and components critical to the assembly were missing. Postaccident metallurgical examination of tail rotor drive shaft assembly, the pulley, and the recovered hardware revealed that tail rotor drive shaft flange was likely directly attached to the air conditioning pulley flange without a drive ring. The bolt length and recovered hardware would have been adequate to secure the drive shaft flange and the pulley flange together to a drive ring; however, the drive ring, two bolts, six washers and one nut were not found amongst the wreckage after a thorough search. The examination also revealed that the two bolts that were recovered failed from fatigue, likely from the cyclic stress due to the absence of a drive ring. According to the helicopter maintenance records, there had been no recent work on the tail rotor drive shaft or air conditioning unit that would have required disassembly and reassembly of the failed flex coupling. ## Factual narrative On September 10, 2022, about 1550, a Bell 206L-1 helicopter, N242BH, was substantially damaged when it was involved in an accident near Banning, California. The pilot and two passengers received minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 firefighting flight. According to the pilot, he was contracted by the California Department of Forestry and Fire Protection (Cal Fire) and was transporting two of their employees to the Banning Municipal Airport (BNG), Banning, California. The pilot had established the helicopter on a final approach path to land between the runway and a taxiway. While on approach, the helicopter made an uncommanded yaw to the right about the vertical axis. The right yaw slowly increased during the approach until he applied full left pedal. The pilot announced to the passengers that he thought he had lost his tail rotor. While about 100 to 150 ft above ground level (agl) he elected not to autorotate while over people and aircraft, and instead kept his power low and kept up his speed. After the helicopter had turned about 180°, the pilot saw a landing area in a back yard and maneuvered the helicopter toward it. As he neared the yard, about 50 ft agl, the helicopter began a continuous right rotation about its vertical axis despite the application of full left pedal. When the helicopter was close to the ground, he applied collective to cushion the landing. The helicopter landed hard, bounced, and rolled onto its left side. Multiple witnesses reported seeing the helicopter “spinning,” followed by a descent to the ground. The pilot turned off the fuel switch and exited the helicopter with assistance from first responders. One passenger exited unassisted and helped the other passenger exit. A review of photographs provided by the pilot showed substantial damage to the main rotor assembly, fuselage, and tailboom. A postaccident examination, which included photographs provided by the pilot, identified all major components near the main wreckage except for some fragments of the main rotor blades that were on a nearby street. The tail rotor drive shaft had separated from the air conditioner pulley flange at the flex coupling (figure 1). Two bolt shank fragments and the attached nuts were found trapped in the two holes of the pulley flange. A bolt head piece, a nut, and six washers were found in the enclosed area. Neither the drive ring, nor any of the hardware other than one nut for connecting the drive shaft flange to the drive ring, were recovered from the fuselage despite a thorough search. Figure 1. View of the separated drive shaft from the pulley at the flex coupling. According to the diagram, 4 nuts, 4 bolts, and a total of 14 washers are required for the drive shaft to pulley flex coupling assembly, as shown in figures 2 and 3. Figure 2. Illustration of a flex coupling for a drive shaft to pulley assembly. Illustration courtesy of Bell. Figure 3. Photograph of an exemplar flexcoupling for a tail rotor drive shaft. Photo courtesy of Bell. The drive shaft section, the pulley, and the recovered hardware were shipped to the National Transportation Safety Board’s Materials Laboratory for further examination. Examination of the drive shaft revealed a complete and intact flex coupling on one end and a separated flex coupling on the other end. The fracture surfaces of the bolt pieces trapped in the pulley flanges had relatively flat features with curving crack arrest lines across most of the fracture surfaces, which are features consistent with a fatigue fracture. A matching fracture surface was observed on the recovered bolt head piece and one of the bolt shanks trapped in the pulley flange. The trapped nut end of one bolt was removed from the pulley flange and mated to the recovered head piece. The total bolt shank length was measured at 0.494 inch between the clamping faces of the head and the nut. The thickness of the pulley flange was 0.164 inch, and the thickness of the flange on the drive shaft assembly was 0.161 inch. For reference, the total thickness of the drive ring adjacent to 1 of the bolts on the intact coupling was 0.119 inch. The 6 recovered washers consisted of 4 washers that were 0.058 inch thick, and 2 washers that were 0.029 inch thick. The specified washers for the pulley flange to drive ring have 2 thicknesses; the thinner washer has a specified nominal thickness of 0.032 inch, and the 3 thicker washers have a specified nominal thickness of 0.063 inch. A maintenance records review revealed no recent work to the tail rotor drive shaft or air conditioning unit. No anomalies were noted in the examination of the maintenance records. ## Aircraft - Registration: [N242BH](https://openairdocs.org/deregistered/N242BH-2024-01-03), registration cancelled 2024-01-03, S/N 45506, built 1980 (OpenAirDocs) - Reported make and model: BELL HELICOPTER TEXTRON 206L-1 - Registry model: [Bell Helicopter Textron 206L-1](https://openairdocs.org/model/bell-helicopter-textron-206l-1) (registry code 1182107) (OpenAirDocs) - Registry engine: [Rolls-Royce 250-C30](https://openairdocs.org/engine/rolls-royce-250-c30) (registry code 54023, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 45506 - Year built: 1980 - Airframe hours: 36275.3 - Engines: ROLLS-ROYC M250-C30P 650 horsepower turbo shaft - Damage: Substantial damage - Flight: Firefighting, Part 91 - Operator: Blue Sky Aviation, doing business as CalFire - Registered owner: B3 Consultants LLC - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, June 28, 2022 - Destination: Same as departure - Airport: BNG, Banning Municipal Airport, runway 08, 4,955 × 100 ft, asphalt - Equipment: Satellite tracking device, Electronic flight bag or handheld device, ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 34; injuries: minor; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane, helicopter; medical: class 1, without waivers/limitations; last flight review May 22, 2022; seat: right; restraint: 4-point; flight hours: 5,594 total, 93 in this make and model, 5,505 as pilot in command, 136 in the last 90 days, 66 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 30° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: 12,000 ft broken - Temperature: 84 °F, dew point 64 °F - Altimeter: 29.89 inHg - Observed at: KHMT, 14 nm away - METAR: KHMT 102215Z AUTO 03006KT 10SM SCT050 BKN120 29/18 A2989 RMK AO2 T02920175 ## Docket (5 files) The files NTSB released with the investigation on April 25, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=105896. 28.3 MB in all. - Materials laboratory factual report 23-007 (item 1, PDF, 5 pages, 5 photos, 686 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15047029&FileExtension=pdf&FileName=23-007-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 11 pages, 6.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16972684&FileExtension=pdf&FileName=Point%20One%20Master_Redacted-Rel.pdf - Pilot's statement (item 3, PDF, 2 pages, 167 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15747499&FileExtension=pdf&FileName=Record%20of%20phone%20Pilots%20Statement-Rel.pdf - Witness statements (item 4, PDF, 26 pages, 19.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16105378&FileExtension=pdf&FileName=Exhibit%20H%20-%20Helibase%20Personnel%20Statements_Redacted-Rel.pdf - Photos (item 5, PDF, 5 pages, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16645767&FileExtension=pdf&FileName=Photos%20for%20WPR22LA340-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.