# NTSB ANC24LA013: Robinson Helicopter R44 II, N74868, Glacier View, AK, February 11, 2024 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: February 11, 2024, 11:30 local (20:30 UTC) - Place: Glacier View, AK - Coordinates: 61.661298, -147.58215 - Nearby events: https://openairdocs.org/map.md?lat=61.6613&lon=-147.5822&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 29, 2026 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Alaska Regional Office - Parties: FAA/FSDO - NTSB case key (mKey): 193797 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC24LA013 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193797/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193797 - Page: https://openairdocs.org/ntsb/ANC24LA013 ## Probable cause A sudden stoppage of the tail rotor for unknown reasons, which resulted in the tortional overload failure of the tail rotor driveshaft. ## 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 · Unknown/Not determined (probable cause); cases with it: [Robinson Helicopter R44 II, 1 case](https://openairdocs.org/ntsb-findings/01046410/cases.md?model=7640122), [All aircraft, 31 cases](https://openairdocs.org/ntsb-findings/01046410/cases.md) - [Tail rotor drive system: tail rotor drive shaft](https://openairdocs.org/ntsb-findings/01046510): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [Robinson Helicopter R44 II, 1 case](https://openairdocs.org/ntsb-findings/01046510/cases.md?model=7640122), [All aircraft, 25 cases](https://openairdocs.org/ntsb-findings/01046510/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) (defining event); cases with it: [Robinson Helicopter R44 II, 9 cases](https://openairdocs.org/ntsb-events/330/sequence.md?model=7640122), [All aircraft, 994 cases](https://openairdocs.org/ntsb-events/330/sequence.md) - [Enroute: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Robinson Helicopter R44 II, 26 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=7640122), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot stated that he was flying the helicopter solo with the doors removed while scouting potential locations for an aerial photography flight scheduled for later that day. During cruise flight, he heard a loud “boom” and felt a slight airframe vibration. He subsequently lost tail rotor thrust and performed an autorotation to an area of snow-covered, mountainous terrain. Examination revealed the tail rotor driveshaft was fractured between the forward and aft flex plates. Further examination of the tail rotor driveshaft revealed the fractures were consistent with ductile tension overload. There was no evidence of pre-existing cracks or other damage to the fracture surfaces. The tail rotor blades were not damaged during the accident sequence, and there were no mechanical anomalies found with the tail rotor gearbox assembly. The torsional twisting of the fractured surfaces of the tail rotor driveshaft is consistent with a sudden binding of the tail rotor gearbox, or a rapid deceleration of the tail rotor blades. There was no damage evident to the tail rotor assembly from a bird strike or impact with a hard object. Although, if a small rag or towel was overlooked during the preflight inspection and it had blown out of the helicopter during the doors-off flight, it likely would have been struck by the tail rotor, resulting in the rapid deceleration of the tail rotor blades, with little to no detectable damage. Thus, the reason for the torsional fracture of the tail rotor driveshaft could not be determined. ## Factual narrative On February 11, 2024, about 1130 Alaska standard time, a Robinson Helicopter R44 II, N74868, was substantially damaged when it was involved in an accident near Glacier View, Alaska. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 business flight. According to the pilot, while in cruise flight with both aft doors removed, about 700 ft above an area of snow-covered glacial terrain, he heard a loud “boom” noise and felt a slight airframe vibration. The pilot stated that he subsequently lost tail rotor thrust and that he then performed an autorotation to an area of snow-covered, mountainous terrain. A postaccident inspection, after the helicopter was recovered, revealed that the tail rotor driveshaft was fractured between the forward and aft flex plates, which resulted in substantial damage to the tail rotor driveshaft system. The fractured pieces of the tail rotor driveshaft were sent to the NTSB Materials Laboratory for further examination. The examination revealed the fractures were consistent with ductile torsion overload. There was no evidence of pre-existing cracks or other damage to the driveshaft surfaces. The tail rotor blades were not damaged. Figure 1. View of the tail rotor driveshaft fracture surfaces The tail rotor gearbox assembly was removed from the accident helicopter and no anomalies were discovered. The pilot stated that he did not have a passenger, but that he did have the doors off in preparation for a passenger/photographer later that day. He also stated that during his preflight inspection, he checked for loose items that could blow out and strike the tail rotor. The pilot did not submit the National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report Form 6120.1. ## Aircraft - Registration: [N74868](https://openairdocs.org/aircraft/N74868), registered now, S/N 11038 (OpenAirDocs) - Reported make and model: ROBINSON HELICOPTER COMPANY R44 II - Registry model: [Robinson Helicopter R44 II](https://openairdocs.org/model/robinson-helicopter-r44-ii) (registry code 7640122) (OpenAirDocs) - Registry engine: [Lycoming IO-540 series](https://openairdocs.org/engine/lycoming-io-540-series) (registry code 41530, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 11038 - Engines: LYCOMING IO-540 SER 300 horsepower reciprocating - Damage: Substantial damage - Flight: Business, Part 91 - Operator: Sheep Mountain Air LLC - Registered owner: Sheep Mountain Air LLC - Airworthiness certificate: Standard, Normal - Departed: PVT, Glacier View, AK - Airport: NONE, Ridgeline - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 39; injuries: none; commercial, remote, flight engineer; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; seat: right; flight hours: 5,000 total ## Weather - Conditions: Visual (VMC), Day - Wind: 240° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 16 °F, dew point 16 °F - Altimeter: 29.49 inHg - Observed at: AZK, 21 nm away - METAR: PAZK 111956Z AUTO 24004KT 10SM CLR M09/M09 A2949 RMK AO2 SLP055 T10891094 FZRANO ## 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 20240211003989A](https://openairdocs.org/incident/20240211003989A), Feb 11, 2024: Robinson Helicopter Company R44 II, Glacier View, AK, Substantial damage. Received report of accident in vicinity of matanuska Glacier involving a Robinson R-44II helicopter operated under part 91 rules. Interview with accident pilot… ## Docket (4 files) The files NTSB released with the investigation on April 22, 2026, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193797. 1.2 MB in all. - FAA inspector's statement (item 1, PDF, 1 page, 63 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19801849&FileExtension=pdf&FileName=Inspector%20Statement-Rel.pdf - Materials laboratory report (item 2, PDF, 1 page, 462 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17346403&FileExtension=pdf&FileName=Email%20Report%20ANC24LA013%20-%20tail%20rotor%20driveshaft-Rel.pdf - Pilot's statement (item 3, PDF, 1 page, 64 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19801948&FileExtension=pdf&FileName=Pilot%20Statment-Rel.pdf - Photos (item 4, PDF, 6 pages, 620 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17346590&FileExtension=pdf&FileName=Photos-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.