# NTSB CEN10LA560: Schweizer 269C, N34LB, Schaumburg, IL, September 20, 2010 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 20, 2010, 17:20 local (22:20 UTC) - Place: Schaumburg, IL - Coordinates: 41.989166, -88.101112 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=41.9892&lon=-88.1011&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-hover: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report May 16, 2011 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Schweizer Aircraft Corporation, Federal Aviation Administration - ADs cited in the narratives: [AD 2001-25-52](https://openairdocs.org/ad/2001-25-52), [AD 2011-01-52](https://openairdocs.org/ad/2011-01-52) (OpenAirDocs) - NTSB case key (mKey): 77406 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN10LA560 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/77406/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=77406 - Page: https://openairdocs.org/ntsb/CEN10LA560 ## Probable cause The in-flight separation of the left aft cluster fitting assembly following the loss of torque on the lock nut due to a manufacturing defect. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Fuselage: fuselage attach fittings sys](https://openairdocs.org/ntsb-findings/01035340): Aircraft › Aircraft structures · Failure (probable cause); cases with it: [Hughes 269C, 1 case](https://openairdocs.org/ntsb-findings/01035340/cases.md?model=4470504), [All aircraft, 5 cases](https://openairdocs.org/ntsb-findings/01035340/cases.md) - [Performance/control parameters](https://openairdocs.org/ntsb-findings/01062000): Aircraft › Aircraft oper/perf/capability · Attain/maintain not possible; cases with it: [Hughes 269C, 3 cases](https://openairdocs.org/ntsb-findings/01062000/cases.md?model=4470504), [All aircraft, 1,269 cases](https://openairdocs.org/ntsb-findings/01062000/cases.md) - [Manufacture/production](https://openairdocs.org/ntsb-findings/04013000): Organizational issues › Development · Manufacturer (probable cause); cases with it: [Hughes 269C, 1 case](https://openairdocs.org/ntsb-findings/04013000/cases.md?model=4470504), [All aircraft, 17 cases](https://openairdocs.org/ntsb-findings/04013000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-hover: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) (defining event); cases with it: [Hughes 269C, 1 case](https://openairdocs.org/ntsb-events/337/sequence.md?model=4470504), [All aircraft, 290 cases](https://openairdocs.org/ntsb-events/337/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Hughes 269C, 10 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=4470504), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis While the helicopter was hovering prior to departure for a routine training flight, a bolt and its associated hardware for the left aft cluster fitting of the tail boom assembly departed the helicopter. Subsequently, the instructor initiated a forced landing and the helicopter came to rest upright. Examination of the bolt and lock nut revealed incomplete threads at the pinch point of the locking stake due to a manufacturing defect. The bolt and lock nut assembly were installed as part of an aft cluster fitting modification that was performed about 4 months and 216 operational hours prior to the accident. As a result of the accident, the Federal Aviation Administration issued an Emergency Airworthiness Directive for owners to check the lock nuts. ## Factual narrative On September 20, 2010, at 1720 central daylight time, a Schweizer 269C single-engine helicopter, N34LB, sustained substantial damage during a forced landing after experiencing a mechanical malfunction while hovering prior to takeoff at the Schaumburg Regional Airport, Schaumburg, Illinois. The helicopter was owned and operated by Bachman Aero, Skokie, Illinois. The certificated flight instructor and pilot receiving instruction were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local flight was originating at the time of the accident. According to the pilot and registered owner, while hovering prior to departure for a routine training flight, a bolt and its associated hardware for the left aft cluster fitting of the tail boom assembly departed the helicopter. The helicopter experienced a vibration and subsequently yawed to the right when the instructor initiated a forced landing. The skids contacted the ground, the helicopter rotated 180 degrees and came to rest upright. Examination of the helicopter revealed the tail boom was partially separated and the tail rotor driveshaft had separated. The bolt and its associated hardware were located on the ramp near the helicopter and were retained for further examination. In addition, the right aft cluster fitting bolt with its associated hardware, which remained attached, were removed and retained for examination. A review of the maintenance records revealed the aft cluster fitting modification kit (Schweizer P/N: SA-269K-0106-1) was installed on the helicopter on June 1, 2010, at a total aircraft time of 1,512.8 hours. On September 10, 2010, 25/50/100/300/400-hour/Annual inspections were performed with no anomalies noted with the aft cluster assembly at a total aircraft time of 1,693.9 hours. The owner stated that since the installation of the aft cluster, the cluster and its components had not been removed or replaced. The airframe had accumulated 1,729.1 total hours at the time of the accident. According to Schweizer Service Letter L-177, AFT CLUSTER FITTING MODIFICATION KIT, dated September 13, 2002, the company developed and approved the cluster modification kit as an alternate means of compliance (AMOC) for the repetitive inspections mandated by the Federal Aviation Administration (FAA) Airworthiness Directive (AD) 2001-25-52. AD 2001-25-52 mandated a repetitive dye penetrant inspection of the aft cluster fittings used on certain Schweizer helicopters. The letter states, "The installation of this kit is recommended at owner's/operator's convenience to provide enhanced aft cluster fitting durability." On December 9, 2010, at the facilities of IMR Test Labs, Lansing, New York, under the supervision of a NTSB senior air safety investigator, the accident nut and bolt assemblies were examined. In addition, two new bolt and nut assemblies that were supplied by Schweizer were examined forcomparison. It was noted that the bolts were Avibank-5 adjustable diameter bolts that were secured with a MS-21043 lock nut torqued to 23-inch pounds (lbs). According to the IMR report, examination of the bolts removed from the accident helicopter showed no anomalies to suggest that they contributed to the loosening. Examination of the lock nut from the loosened left side fastener revealed incomplete threads at the pinch point of the locking stake. Torque testing showed the loosened left side lock nut had no prevailing torque. The prevailing torque should have been between 2 to 18 in-lbs. On December 20, 2010, the FAA issued Emergency AD 2011-01-52, which required before further flight, unless previously accomplished, the removal of the lock nut. The lock nut should then be reinstalled while determining the lock nut drag torque. If the drag torque is a minimum of 2 in-lbs, retorquing the locknut to 23 in-lbs is required. If the drag torque is not at least 2 in-lbs, the replacement of the lock nut with an airworthy lock nut is required. ## Aircraft - Registration: [N34LB](https://openairdocs.org/aircraft/N34LB), registered now, S/N 780714, built 1978 (OpenAirDocs) - Reported make and model: SCHWEIZER 269C - Registry model: [Hughes 269C](https://openairdocs.org/model/hughes-269c) (registry code 4470504) (OpenAirDocs) - Registry engine: [Lycoming HIO-360-D1A](https://openairdocs.org/engine/lycoming-hio-360-d1a) (registry code 41893, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 780714 - Airframe hours: 1759 - Engines: Lycoming HIO-360 190 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: Bachman Aero - Registered owner: Bachman Aero - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, September 10, 2010, 65 hours before - Departed: 06C, Schaumburg, IL - Destination: 06C, Schaumburg, IL - Airport: 06C, Schaumburg Regional Airport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 23; injuries: none; flight instructor, private, commercial; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review June 22, 2010; seat: right; flight hours: 409 total, 240 in this make and model, 275 as pilot in command, 119 in the last 90 days, 53 in the last 30 days, 5 in the last 24 hours - Student pilot; age 29; injuries: none; commercial, foreign; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; seat: left; flight hours: 16 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 75 °F - Observed at: DPA, 8 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 20100920047219A](https://openairdocs.org/incident/20100920047219A), Sep 20, 2010: Hughes 269C, Schaumburg, IL, Substantial damage. This was the third flight of the day. The student pilot performed the preflight inspection under the supervision of the flight instructor. The student pilot… ## Docket (7 files) The files NTSB released with the investigation on February 1, 2011, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=77406. 3.4 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 307 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341561&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - IMR Test Lab Report (item 2, .PDF, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341563&FileExtension=.PDF&FileName=IMR%20Test%20Lab%20Report-Redacted.PDF - NTSB Materials Laboratory Chief Concurrence Statement (item 3, .PDF, 88 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341565&FileExtension=.PDF&FileName=NTSB%20Materials%20Laboratory%20Chief%20Concurrence%20Statement-Master.PDF - Maintenance Records (item 4, .PDF, 39 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341566&FileExtension=.PDF&FileName=Maintenance%20Records-Redacted.PDF - Schweizer Service Letter L-177 (item 5, .PDF, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341567&FileExtension=.PDF&FileName=Schweizer%20Service%20Letter%20L-177-Master.PDF - FAA Emergency AD 2011-01-52 (item 6, .PDF, 36 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341568&FileExtension=.PDF&FileName=FAA%20Emergency%20AD%202011-01-52-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 7, .PDF, 327 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40341569&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.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.