# NTSB ANC13TA076: Bell UH-1B, N70NW, Tok, AK, August 8, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Final report - Date: August 8, 2013, 14:30 local (22:30 UTC) - Place: Tok, AK - Coordinates: 61.259944, -149.600173 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=61.2599&lon=-149.6002&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report August 7, 2014 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: Bell Helicopter, Federal Aviation Administration - NTSB case key (mKey): 87720 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC13TA076 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87720/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87720 - Page: https://openairdocs.org/ntsb/ANC13TA076 ## Probable cause The failure of the tail rotor crosshead bearing, which resulted in a loss of tail rotor control. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor drive system: tail rotor gearbox](https://openairdocs.org/ntsb-findings/01046520): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [All aircraft, 12 cases](https://openairdocs.org/ntsb-findings/01046520/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 tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) (defining event); cases with it: [All aircraft, 100 cases](https://openairdocs.org/ntsb-events/242/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot had just completed a water drop with a long-line and water bucket when he noticed a degradation of the helicopter's directional control. He returned to the airport, released the bucket, and attempted a "stuck-pedal" run-on landing. During the attempted landing, the helicopter began to drift left toward trees. Unable to maintain directional control, the pilot initiated a go-around, and the main rotor blades then struck the treetops. After realigning with the runway, he executed a "slow-speed" run-on landing to a gravel area adjacent to the runway. During touchdown, the helicopter bounced multiple times, and it then came to rest upright. The helicopter sustained substantial damage to the fuselage, vertical fin, and tail rotor blades. A postaccident examination of the tail rotor assembly revealed that the tail rotor crosshead bearing's split inner ring's inboard shoulder was spalled and completely worn away, which allowed the outboard set of bearing balls to run over the pitch change rod's seating flange for the split inner ring's inboard shoulder. The pitch change rod was then free to migrate outboard, and it machined a hole through the end of the crosshead. The movement of the pitch change rod decreased the effectiveness of the left antitorque pedal and increased the effectiveness of the right antitorque pedal. ## Factual narrative On August 8, 2013, about 1430 Alaska daylight time, a restricted category Bell UH-1B helicopter, N70NW, sustained substantial damage during a forced landing, after a loss of tail rotor effectiveness at the Tok Junction Airport, Tok Alaska. The helicopter was being operated by Northern Pioneer Helicopters, Big Lake, Alaska, as a 14 CFR Part 133 external load, aerial firefighting flight when the accident occurred. The certificated commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and the U.S. Forestry Service's flight following procedures were in effect. The local flight departed Tok Junction Airport, about 1400. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on August 9, the pilot reported that the helicopter was dispatched to Tok Junction in support of firefighting operations for the U.S. Forestry Service. The pilot said that during the accident flight, he had just completed a water drop using a water bucket and a 100-foot long-line attached to the helicopter's belly-mounted cargo hook. Immediately after releasing the load of water at a predetermined site, he noticed a degradation of directional control. He said that he was able to maintain control of the helicopter, and he subsequently returned to the Tok Junction Airport with the 100-foot long-line and water bucket still attached to the helicopter. As the helicopter approached the airport, the pilot jettisoned the 100 foot long-line and water bucket before attempting an emergency, stuck pedal run-on landing. During the emergency landing approach, the helicopter began to drift to the left, towards a stand of trees. Unable to maintain directional control, he initiated a go-around, and the main rotor blades struck the tops of the trees. After realigning the helicopter with the runway, he performed a "slow-speed" run-on landing to a gravel area adjacent to the runway. During touchdown, the helicopter bounced multiple times and came to rest upright. The helicopter sustained substantial damage to fuselage, vertical fin and tail rotor blades. The helicopter was equipped with after-market tail rotor blades. An on-scene examination of the tail rotor assembly by the operator revealed that the pitch change rod, and the crosshead bearing retention nut were protruding outboard through the tail rotor crosshead. The entire tail rotor gearbox assembly was removed from the accident helicopter for further examination. On January 14 and 15, 2014, under the supervision of the NTSB IIC, the tail rotor pitch change assembly was examined at Bell Helicopter's field investigation laboratory, Hurst, Texas. The examination revealed that the tail rotor crosshead bearing's inboard shoulder of the split inner ring was spalled, and completely worn away, allowing the bearings outboard set of bearing balls to run over the pitch change rod's seating flange for the split inner ring inboard shoulder. The pitchchange rod was then free to migrate outboard machining a hole through the end of the crosshead. As a result of the pitch change rod moving outboard, a decrease in the amount of maximum tail rotor blade pitch change occurred. ## Aircraft - Registration: N70NW (not matched to a registry record) - Reported make and model: BELL UH-1B - Category: Helicopter - Serial number: 60-3568 - Airframe hours: 11144 - Engines: LYCOMING T-53L13B 1400 horsepower turbo shaft - Damage: Substantial damage - Flight: External load, Part 133 - Operator: Northern Pioneer Helicopters LLC - Registered owner: Northern Pioneer Helicopters LLC - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, July 27, 2013 - Departed: PFTO, Tok, AK - Destination: PFTO, Tok, AK - Flight plan: Company VFR - Airport: PFTO, Tok Junction, runway 25, 2,509 × 50 ft, gravel ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 43; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land, single-engine sea; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review May 10, 2013; seat: left; restraint: lap only; flight hours: 500 total ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: 11,000 ft broken - Temperature: 70 °F, dew point 45 °F - Altimeter: 29.76 inHg - Observed at: PAOR, 36 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 20130808015749A](https://openairdocs.org/incident/20130808015749A), Aug 8, 2013: Bell UH-1B, Tok, AK, Substantial damage. While doing bucket drops on fire # 414 ( after approx. 6 drops ) PIC noticed the aircraft was not getting enough right pedal. PIC contacted Tok forestry div z… ## Docket (2 files) The files NTSB released with the investigation on June 2, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87720. 3.5 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 3.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40412904&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 2, .PDF, 243 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40412905&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-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.