# NTSB DEN99LA168: Bell 47G3B2A, N83246, Tremonton, UT, September 23, 1999 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 23, 1999, 09:00 local (15:00 UTC) - Place: Tremonton, UT - Coordinates: 41.690769, -112.269325 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=41.6908&lon=-112.2693&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report June 23, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 47427 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN99LA168 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/47427/pdf - Page: https://openairdocs.org/ntsb/DEN99LA168 ## Probable cause The pilot's failure to maintain rotor rpm while attempting a precautionary autorotation landing. A factor was the loss of engine power for undetermined reasons. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - nonmechanical, cruise - reason for occurrence undetermined (contributing factor) - autorotation - attempted, pilot in command - Loss of engine power(total) - nonmechanical, emergency descent/landing - rotor rpm - not maintained, pilot in command (cause) - Hard landing, emergency descent/landing - terrain condition - crop ## Analysis The pilot departed the airport en route to a local staging area to perform aerial application work. He departed with 30 gal. of fuel and was planning to pick up a load of chemical spray at his destination. Approximately 2 1/2 miles southeast of the airport, the engine began to miss. He decided to make a precautionary landing in an alfalfa field. When the helicopter was 200 ft. agl, the engine began to run rougher and he initiated an autorotation. He closed the throttle and the engine quit. The helicopter impacted the ground, stopped suddenly and rocked forward. The rotor blades flexed downward, severing the tail boom. The day following the accident, an examination of the engine was performed by an FAA maintenance inspector and no discrepancies were found. When asked what recommendation the pilot could make as to how the accident could have been prevented, he responded that he could have 'performed [a] better autorotation.' ## Factual narrative On September 23, 1999, approximately 0900 mountain daylight time, a Bell 47G3B2A helicopter, N83246, registered to and operated by the pilot and doing business as Helowood Helicopters, was substantially damaged during a forced landing following a loss of engine power while maneuvering 2 miles southeast of Tremonton, Utah. The commercial pilot, the sole occupant aboard, was not injured. The aircraft was being operated as a ferry flight under Title 14 CFR Part 91, and a company VFR flight plan had been filed. The flight originated from the Tremonton Municipal Airport, Tremonton, Utah, 5 minutes prior to the accident, and was en route to Coalville, Utah. Visual meteorological conditions prevailed. According to the pilot, he was flying to a local staging area for the purpose of conducting aerial application work. He departed with 30 gallons of fuel and was planning to pick up a load of chemical spray at his destination. Approximately two and a half miles southeast of Tremonton, the engine began "running rough," and he attempted to return to the airport. The engine continued to "miss," and one half a mile after turning around he decided to make a precautionary landing in an alfalfa field. At that time, "the engine was running well enough to land with power." However, when the helicopter was 200 feet above ground level (agl), the engine began to run rougher and he initiated an autorotation. He closed the throttle completely and the engine quit. The helicopter touched down with a forward airspeed of 2 to 3 miles per hour. The aircraft stopped suddenly and rocked forward. The rotor blades flexed downward, severing the tail boom. The day following the accident, an examination of the engine was performed by an FAA maintenance inspector. According to the inspector's statement, he removed the rear spark plugs and they appeared to be in satisfactory condition. A compression test was performed and no discrepancies were noted. No apparent damage to the cylinders was observed. The magnetos were satisfactorily checked for timing, and the carburetor was found to be securely and accurately installed. The maintenance records were reviewed and found to be "complete and satisfactory." Fuel samples were taken from the carburetor and were found to be clear and free of contaminates. The engine was unable to be functionally tested due to the damage caused by the main rotor blades. According to the inspector, "No cause could be determined for the engine's unsatisfactory performance" (see attached statement). When asked in the NTSB Pilot/Operator Aircraft Accident Report (Form 6120.1/2) what recommendation the pilot could make as to how the accident could have been prevented, he responded that he could have "performed [a] better autorotation." ## Aircraft - Registration: [N83246](https://openairdocs.org/deregistered/N83246-2022-07-30), registration cancelled 2022-07-30, S/N 6858, built 1973 (OpenAirDocs) - Reported make and model: Bell 47G3B2A - Registry model: [Bell 47G3B2A](https://openairdocs.org/model/bell-47g3b2a) (registry code 1181025) (OpenAirDocs) - Registry engine: [Lycoming TVO-435-GIA](https://openairdocs.org/engine/lycoming-tvo-435-gia) (registry code 41526, turbo-prop) (OpenAirDocs) - Category: Helicopter - Serial number: 6858 - Airframe hours: 9912 - Engines: Lycoming TVO-435-F1A 280 horsepower reciprocating - Damage: Substantial damage - Flight: Ferry, Part 137 - Registered owner: Brent V. Wood - Airworthiness certificate: Special, Restricted (Special); Standard, Normal - Last inspection: 100 hour, August 11, 1999, 13 hours before - Departed: U27, UT - Destination: NONE, COALVILLE, UT - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 17,000 total, 17,000 in this make and model, 85 in the last 90 days, 22 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 52 °F, dew point 43 °F - Altimeter: 30.00 inHg - Observed at: LGU, 16 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 19990923027879A](https://openairdocs.org/incident/19990923027879A), Sep 23, 1999: Bell 47G3B2A, Tremonton, UT, Substantial damage. (.19) On September 23, 1999, approx. 0900 mountain daylight time, a Bell 47G3B2A helicopter, N83246, registered to and operated by the pilot, was substantially… 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.