# NTSB FTW02LA177: Bell 47G-3B-1, N999DW, Nederland, CO, June 8, 2002 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 8, 2002, 10:30 local (16:30 UTC) - Place: Nederland, CO - Coordinates: 40.667778, -106.052497 - Nearby events: https://openairdocs.org/map.md?lat=40.6678&lon=-106.0525&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 1, 2003 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 54881 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW02LA177 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/54881/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=54881 - Page: https://openairdocs.org/ntsb/FTW02LA177 ## Probable cause the pilot's inadvertent in-flight encounter with severe turbulence, which resulted in main rotor-tailboom contact and the separation of the tailrotor drive shaft. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - In flight encounter with weather, cruise - flight into adverse weather - inadvertent, pilot in command (cause) - weather condition - turbulence (cause) - misc rotorcraft,main rotor/tail boom contact - rotor drive system,tail rotor drive shaft - separation - Forced landing, descent - emergency - autorotation - performed, pilot in command ## Analysis Prior to the flight in mountainous terrain, the pilot obtained a weather forecast that called for winds from the southwest at 30 mph, with gusts up to 40 mph. The flight departed and was in cruise flight at 9,000 feet (700 feet agl) with a 20-25 knot headwind and experiencing light turbulence, when the flight encountered "severe turbulence." The pilot stated that the helicopter went "up and down violently for a period of 2-3 seconds." The tailrotor drive shaft was severed by the main rotor blades, and the helicopter then experienced "a right yaw that full application of left pedal would not correct." The pilot stated that during the event the engine and rotor rpm increased past their upper limits. He was able to bring the engine and rotor rpm within limits and regained control of the helicopter. Subsequently, the pilot performed an autorotation to sloping terrain without further incident. According to a witness, who was fishing on a lake 4 miles from the accident site, he observed water spouts between 2 and 8 feet tall and high swirling winds near the time of the accident. ## Factual narrative On June 8, 2002, at 1030 mountain daylight time, Bell 47G-3B-1 helicopter, N999DW, was substantially damaged when it encountered turbulence while in cruise flight near Nederland, Colorado. The helicopter was registered to and operated by the pilot. The private pilot, sole occupant of the helicopter, was not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight originated from the pilot's private staging area in Nederland at 0900. According to the pilot, he obtained weather from a television station in Denver, Colorado. The weather forecast called for winds from the southwest at 30 mph, with gusts up to 40 mph. The flight departed, flew approximately 1.5 hours , and was in cruise flight at 9,000 feet (700 feet agl) with a 20-25 knot headwind experiencing light turbulence, when the flight encountered "severe turbulence." The pilot stated that the helicopter went "up and down violently for period of 2-3 seconds." The tailrotor driveshaft was severed by the main rotor, and the helicopter then experienced "a right yaw that full application of left pedal would not correct." The pilot stated that during the event the engine and rotor rpm increased past their upper limits. He was able to bring the engine and rotor rpm within limits and regained control of the helicopter. Subsequently, the pilot performed an autorotation to sloping terrain without further incident. The pilot examined the helicopter and reported that the tailrotor drive shaft was separated, the tailboom was damaged, and one main rotor blade was damaged. According to a witness, who was fishing on a lake 4 miles from the accident site, he observed water spouts between 2 and 8 feet tall and high swirling winds near the time of the accident. The witness further stated that "in 26 years of backpacking to high lakes I had never seen this happen." ## Aircraft - Registration: N999DW (not matched to a registry record) - Reported make and model: Bell 47G-3B-1 - Category: Helicopter - Serial number: 6604 - Airframe hours: 4123 - Engines: Lycoming TVO-435-D1B 270 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Bernard P. Gateau - Airworthiness certificate: Standard, Normal - Last inspection: Annual, July 10, 2001, 75.6 hours before - Departed: NONE, Nederland, CO ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; last flight review July 9, 2001; seat: left; flight hours: 553 total, 74 in this make and model, 417 as pilot in command, 21 in the last 90 days, 10 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 200° at 20 knots, gusting 25 - Lowest ceiling: none - Temperature: 64 °F ## 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 20020608013909A](https://openairdocs.org/incident/20020608013909A), Jun 8, 2002: Bell 47G3B1, Nederland, CO, No damage. (-23) June 8, 2002, at 1020 mtn time, Bell 47G-3B-1 helicopter, N999DW, was substantially damaged when it encountered turbulence while in cruise flt near… ## Docket (5 files) The files NTSB released with the investigation on November 21, 2002, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=54881. 1.4 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 634 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40443330&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Witness Statement (item 2, .PDF, 76 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40443331&FileExtension=.PDF&FileName=Witness%20Statement-Redacted.PDF - Photo 1: View of helicopter. Arrow points to the separated tailrotor drive shaft. (Courtesy Owner, No Negative) (item 3, .PDF, 334 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40169761&FileExtension=.PDF&FileName=Photo%201%3A%20View%20of%20helicopter.%20Arrow%20points%20to%20the%20separated%20tailrotor%20drive%20shaft.%20(Courtesy%20Owner,%20No%20Negative)-Master.PDF - Photo 2: Close-up view of the separated tailrotor drive shaft and the tailboom damage. (Courtesy Owner, No Negative) (item 4, .PDF, 177 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40169762&FileExtension=.PDF&FileName=Photo%202%3A%20Close-up%20view%20of%20the%20separated%20tailrotor%20drive%20shaft%20and%20the%20tailboom%20damage.%20(Courtesy%20Owner,%20No%20Negative)-Master.PDF - Photo 3: Close-up view of the main rotor blade damage. (Courtesy Owner, No Negative) (item 5, .PDF, 145 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40169763&FileExtension=.PDF&FileName=Photo%203%3A%20Close-up%20view%20of%20the%20main%20rotor%20blade%20damage.%20(Courtesy%20Owner,%20No%20Negative)-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.