# NTSB SEA97LA112: Bell 47G-3B, N8491E, Snohomish, WA, May 15, 1997 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: May 15, 1997, 16:10 local (23:10 UTC) - Place: Snohomish, WA - Coordinates: 47.94017, -121.999305 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.9402&lon=-121.9993&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report July 13, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 42606 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA97LA112 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42606/pdf - Page: https://openairdocs.org/ntsb/SEA97LA112 ## Probable cause the pilot's encounter with of a loss of tail rotor effectiveness (LTE) situation, and his subsequent inadequate remedial action. Related factors included: wind conditions that were conducive to an unanticipated right yaw event, and the pilot's limited experience in helicopters. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of control - in flight, landing - aborted - weather condition - unfavorable wind (contributing factor) - loss of tail rotor effectiveness - encountered, pilot in command (cause) - remedial action - inadequate, pilot in command (cause) - lack of total experience in kind of aircraft, pilot in command (contributing factor) - In flight collision with terrain/water, descent - uncontrolled ## Analysis The pilot was in a commercial helicopter pilot upgrade training program. He was not yet rated for helicopters, but did hold an instructor's endorsement granting helicopter solo privileges. At the time of the accident, he was aborting a practice landing in wind conditions which were conducive to an unanticipated right yaw (also known as loss of tail rotor effectiveness, or LTE) event. As he completed a turn to downwind, the helicopter made an uncommanded right turn. Despite the application of left pedal and forward cyclic by the pilot, the helicopter 'continued to rotate violently until impact on the left side.' FAA inspectors, who examined the helicopter at the accident site, reported that they found no evidence of a mechanical malfunction; they stated that the tail rotor system was intact. ## Factual narrative On May 15, 1997, approximately 1610 Pacific daylight time, a Bell 47G-3B helicopter, N8491E, crashed approximately 1 1/2 miles southeast of Harvey Field, Snohomish, Washington. The helicopter was substantially damaged and the pilot, who held a commercial certificate with an airplane category rating and had solo privileges for helicopters, received minor injuries. The local 14 CFR 91 instructional solo practice flight, which the pilot was conducting as part of a commercial helicopter pilot upgrade training program, originated at Harvey Field. Visual meteorological conditions existed and no flight plan had been filed for the flight. The pilot reported that he was attempting a practice landing on an island in the Snohomish River at the time of the accident. He stated that he got high on his approach, to the point where a steep descent to his intended landing spot would be required, and decided to terminate the approach. As he accelerated through about 40 MPH at about 40 to 50 feet above ground level, he began a turnout to the left, toward downwind. The pilot reported that after completing the downwind turn, the helicopter made an uncommanded turn to the right. The pilot stated that despite the application of left pedal and forward cyclic, "the helicopter continued to rotate violently until impact on the left side." FAA inspectors responded to the accident site and performed an on-site examination of the helicopter wreckage. They reported to the NTSB that the on-site examination revealed no evidence of a mechanical malfunction in the helicopter, and that the tail rotor was found intact. In a telephone conversation with the pilot on May 15, 1997, the pilot stated that at the time of the occurrence, he was heading "parallel with the trees" (roughly southeast.) The Seattle Sectional Aeronautical Chart depicts the Snohomish River coursing approximately to the south-southeast in the accident area. The pilot further reported on his accident reported that winds in the accident area were from 310 degrees at 8 to 12 knots. The reported relative wind direction and velocity is within a region conducive to a "weathercock stability" unanticipated right yaw (also referred to as loss of tail rotor effectiveness, or LTE) event as defined in FAA Advisory Circular (AC) 90-95, "Unanticipated Right Yaw in Helicopters." The AC states that unanticipated right yaw events can result in loss of control of the helicopter if the pilot does not apply timely corrective action (consisting of simultaneous application of full left pedal and forward cyclic, and if altitude permits, a reduction in power and collective pitch, followed by adjusting controls for normal forward flight as recovery is effected.) ## Aircraft - Registration: [N8491E](https://openairdocs.org/deregistered/N8491E-2018-01-26), registration cancelled 2018-01-26, S/N 2712, built 1961 (OpenAirDocs) - Reported make and model: Bell 47G-3B - Registry model: [Bell 47G-3B](https://openairdocs.org/model/bell-47g-3b) (registry code 1181026) (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: 2712 - Airframe hours: 4004 - Engines: Lycoming TV0-435-B1A 270 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Registered owner: Steve L. Gable - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, February 2, 1997, 50 hours before - Departed: S43, WA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 32; commercial; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 775 total, 36 in this make and model, 623 as pilot in command, 60 in the last 90 days, 28 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 310° at 10 knots - Visibility: 20 statute miles - Lowest ceiling: 15,000 ft overcast - Temperature: 61 °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 19970515010809A](https://openairdocs.org/incident/19970515010809A), May 15, 1997: Bell 47G3B, Snohomish, WA, Substantial damage. (.4) The pilot was in a commercial helicopter pilot upgrade training program. He was not yet rated for helicopters, but did hold an instructor's endorsement… ## Other investigations on N8491E (2) 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. - [NTSB SEA69A0012](https://openairdocs.org/ntsb/SEA69A0012), Aug 13, 1968: Bell 47G-3B (N8491E), Twin Falls, ID, substantial damage - [NTSB UNK64X2017](https://openairdocs.org/ntsb/UNK64X2017), May 30, 1964: Bell 47G3B (N8491E), Muldoon, ID, substantial damage 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.