# NTSB WPR14LA374: Bell 206, N64AW, Tombstone, AZ, September 12, 2014 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 12, 2014, 11:15 local (18:15 UTC) - Place: Tombstone, AZ - Coordinates: 31.701389, -110.053611 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=31.7014&lon=-110.0536&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report April 20, 2016 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Rolls-Royce Corporation, Airwest Helicopters, Federal Aviation Administration, Bell Helicopter - NTSB case key (mKey): 90067 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR14LA374 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/90067/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=90067 - Page: https://openairdocs.org/ntsb/WPR14LA374 ## Probable cause A partial loss of engine power during cruise flight due to loose “B” nut fittings and a bent tube as a result of maintenance personnel’s inadequate inspection of the nuts during the most recent inspection. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Misc hardware: fasteners](https://openairdocs.org/ntsb-findings/01071430): Aircraft › Fluids/misc hardware · Incorrect service/maintenance (probable cause); cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-findings/01071430/cases.md?model=1182110), [All aircraft, 58 cases](https://openairdocs.org/ntsb-findings/01071430/cases.md) - [Misc hardware: hoses and tubes](https://openairdocs.org/ntsb-findings/01071410): Aircraft › Fluids/misc hardware · Incorrect service/maintenance (probable cause); cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-findings/01071410/cases.md?model=1182110), [All aircraft, 40 cases](https://openairdocs.org/ntsb-findings/01071410/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell 206-L4, 2 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=1182110), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Other (probable cause); cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=1182110), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Misc hardware: fasteners](https://openairdocs.org/ntsb-findings/01071430): Aircraft › Fluids/misc hardware · Related operating info; cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-findings/01071430/cases.md?model=1182110), [All aircraft, 58 cases](https://openairdocs.org/ntsb-findings/01071430/cases.md) - [Misc hardware: fasteners](https://openairdocs.org/ntsb-findings/01071430): Aircraft › Fluids/misc hardware · Related maintenance info; cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-findings/01071430/cases.md?model=1182110), [All aircraft, 58 cases](https://openairdocs.org/ntsb-findings/01071430/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Bell 206-L4, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=1182110), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Enroute-cruise: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell 206-L4, 2 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1182110), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Bell 206-L4, 5 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=1182110), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The commercial pilot reported that, after initiating a climb for the local flight, he observed that the helicopter was not producing adequate power. He found a suitable landing site and descended toward it. When the helicopter was about 60 to 70 ft above the ground, the helicopter started descending rapidly and impacted the ground hard. During a pressure leak check of the engine, air leaks at three separate "B" nut fittings were found; two of the leaks were at the power turbine governor, and one leak was at the gas producer fuel control. The engine was test run, and it operated; however, it then lost power consistent with the pilot's report. Further examination of the "B" nut fittings revealed that one of the "B" nuts was less than finger tight, the second one was just above finger tight, and the third exhibited breakaway torque within the specified range. The "B" nut fittings were tightened to specifications and rechecked. One of the leaks was still present; the tube was removed, and it was bent near where the leak was found. A new tube was installed, and the engine was run again with no anomalies noted. The engine manufacturer had previously issued several commercial service letters regarding the importance of properly torqueing and aligning the fuel, lubrication, and pneumatic systems tubes and fittings; the service letters contained proper directions, placards, and 100-hour-inspection requirements. The helicopter's most recent 100-hour inspection occurred about 66 hours before the accident. It is likely that the "B" nuts became loose during the approximate 66 hours of operation since the most recent inspection and that maintenance personnel did not adequately inspect the "B" nuts at that inspection and, thus, failed to detect that they were not properly torqued. It could not be determined when the tube became bent. ## Factual narrative On September 12, 2014 about 1115 mountain standard time, the pilot of a Bell 206L4, N64AW, initiated a forced landing onto a gravel road following a partial loss of power near Tombstone, Arizona. The helicopter was registered to, and operated by, Airwest Helicopters LLC under the provisions of Title 14 Code of Federal Regulations Part 135. The commercial pilot and one passenger were uninjured; the helicopter sustained substantial damage to the tailboom. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed. The flight originated from Sierra Vista Municipal Airport – Libby Army Airfield (FHU), Sierra Vista, Arizona at 1050 for a local flight. The pilot reported that about 20 minutes into the flight, he started a climb at about 60 knots indicated airspeed (KIAS). As the torque reached 85%, he observed the power turbine RPM (N2) and the main rotor RPM (Nr) at 95%. The turbine outlet temperature (TOT) was approximately 680 degrees; otherwise, all other indications were normal. The pilot reduced collective until N2/Nr returned to 100 percent; torque was about 60%. The pilot increased power to 70% torque, and the N2/Nr decreased to 95%. The pilot lowered the collective a second time and the N2/Nr went back to 100%. The pilot found a suitable landing site and he descended at about 70 KIAS while maintaining 95% N2/Nr at about 40% torque. When the helicopter was about 60-70 feet above the ground the pilot decelerated the helicopter; the helicopter descended rapidly and impacted the ground hard. Subsequently, the main rotor blade severed the tailboom. During a postaccident examination the engine was removed from the airframe and transported to a facility for an engine run. Prior to engine start, a pressure air leak check was performed and three air leaks were observed at three separate "B" nut fittings. Two of the leaks were at the power turbine governor, and one was at the gas producer fuel control. The engine was started and operated, however a power loss was experienced similar to what the pilot described. The engine was shut down, and the "B" nut fittings were further examined; one of the "B" nuts was less than finger tight, a second one was just above finger tight, and the third exhibited breakaway torque within the specified range. All of the fittings displayed a torque stripe and each had a visible crack in the paint between the "B" nut and fitting. The three "B" nuts were torqued to specifications and rechecked. One of the leaks was still leaking; the line was removed and visually inspected. There was a bend near the end of the line, where the leak was observed. A new line was installed, torqued to specification, and checked for leaks. With no leaks observed, the engine was run a second time and it ran normally with no anomalies noted. Review of the helicopter's maintenance logs revealed that the helicopter's most recent maintenance was a 100 hour inspection that was completed on July 11, 2014 at anaircraft total time of 4230.8 hours. The accident occurred about 66 hours later, at a total time of 4,297 hours. Rolls-Royce has issued several Commercial Service Letters since September 1987 regarding improper torque or alignment of the fuel, lube, and air systems tubes and fittings. These service letters highlighted the commonly seen issues and urged compliance with the appropriate engine operation and maintenance manuals. Also in these service letters, Rolls-Royce issued placards, warning labels, and maintenance checks every 100 hours. ## Aircraft - Registration: [N64AW](https://openairdocs.org/aircraft/N64AW), registered now, S/N 52298, built 2004 (OpenAirDocs) - Reported make and model: BELL 206 (L4) - Registry model: [Bell 206-L4](https://openairdocs.org/model/bell-206-l4) (registry code 1182110) (OpenAirDocs) - Registry engine: [Rolls-Royce 250 20&30 series](https://openairdocs.org/engine/rolls-royce-250-20-30-series) (registry code 54584, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 52298 - Year built: 2004 - Airframe hours: 4297 - Engines: ROLLS-ROYCE 250 C30P 650 horsepower turbo shaft - Damage: Substantial damage - Flight: Part 135 - Operator: Airwest Helicopters LLC - Registered owner: Airwest Helicopters LLC - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, July 11, 2014, 67 hours before - Departed: FHU, Sierra Vista, AZ - Destination: FHU, Sierra Vista, AZ - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 64; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review February 4, 2014; seat: right; restraint: 3-point; flight hours: 10,800 total, 1,650 in this make and model, 9,800 as pilot in command, 55 in the last 90 days, 15 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 82 °F, dew point 57 °F - Altimeter: 30.10 inHg - Observed at: FHU, 16 nm away ## Docket (9 files) The files NTSB released with the investigation on March 7, 2016, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=90067. 7.6 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 372 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437287&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Google Earth - Accident Site (item 2, .PDF, 256 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437288&FileExtension=.PDF&FileName=Google%20Earth%20-%20Accident%20Site-Master.PDF - Record of Conversation - Federal Aviation Administration regarding the Engine Run (item 3, .PDF, 91 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437289&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20Federal%20Aviation%20Administration%20regarding%20the%20Engine%20Run-Master.PDF - Rolls-Royce Commercial Service Letters (item 4, .PDF, 434 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437290&FileExtension=.PDF&FileName=Rolls-Royce%20Commercial%20Service%20Letters-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 5, .PDF, 637 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437291&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Reports from Parties to the Investigation - Rolls Royce w/photos (item 6, .PDF, 4.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437292&FileExtension=.PDF&FileName=Reports%20from%20Parties%20to%20the%20Investigation%20-%20Rolls%20Royce%20w%2Fphotos-Master.PDF - Reports from Parties to the Investigation - Bell Helicopter (item 7, .PDF, 5 photos, 492 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437293&FileExtension=.PDF&FileName=Reports%20from%20Parties%20to%20the%20Investigation%20-%20Bell%20Helicopter-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 8, .PDF, 315 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437294&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - On Scene Photographs - Courtesy of Law Enforcement (item 9, .PDF, 2 photos, 830 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437295&FileExtension=.PDF&FileName=On%20Scene%20Photographs%20-%20Courtesy%20of%20Law%20Enforcement-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.