NTSB CAROL · Event
Event SEA94LA029
Aircraft involved
Probable cause & findings
TRANSMISSION SHEAR BOLTS FAILED CAUSING A LOSS OF POWER TO THE ROTOR SYSTEM, AND THE PILOT ENCOUNTERED UNSUITABLE TERRAIN DURING HIS AUTOROTATION ATTEMPT.
Factual narrative
On November 9, 1993, at 0930, a Bell B-47G3B2, N8169J, operated by Farm & Forest Helicopter Service, impacted terrain at Toledo, Washington, during an emergency forced landing. There was no flight plan filed for the local external load flight, conducted under 14 CFR 133, that was on takeoff from a field site when the accident occurred. The commercial certificated pilot was not injured in the accident. The aircraft was substantially damaged. There was no fire. The pilot reported he was on takeoff with an external load of Christmas trees when he heard a grinding sound and the main rotor RPM began to decrease. He initiated an autorotation from about 40 to 50 feet into the christmas trees. On landing, the tair boot hit a tree and bent. An examination of the wreckage revealed fractured main transmission shear bolts. The pilot attributed the failure to power impulses after repeated compressor stalls or partial flame-outs of the turbine engine. WHILE LIFTING CHRISTMAS TREES UNDER EXTERNAL LOAD CONDITIONS THE PILOT HEARD A CLUNK AND EXPERIENCED A LOSS OF POWER. HE ATTEMPTED AN AUTOROTATION FROM 40 TO 50 FEET INTO THE CHRISTMAS TREE FARM, STRIKING AND BENDING THE TAIL BOOM WHEN IT IMPACTED A TREE. INVESTIGATION REVEALED THAT THE TRANSMISSION SHEAR BOLTS, PN 47-620-485-9, HAD SHEARED. THE PILOT ATTRIBUTED THE FAILURE OF THE SHEAR BOLTS TO POWER IMPULSES FROM REPEATED COMPRESSOR STALLS. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12
Verbatim from NTSB's published report. Source file
NTSB_1993_SEA94LA029.txt.
Findings + structured fields enriched from FAA avall.mdb.
Full investigation docket on
data.ntsb.gov ↗.
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Related research
What the literature says.
Academic papers and agency reports matching this event's aircraft type or causal vocabulary (stall). Sourced from NASA NTRS, NTSB Safety Studies, FAA CAMI, AOPA Air Safety Institute, Embry-Riddle Scholarly Commons, arXiv, and the Semantic Scholar academic graph.
- NASA NTRS 2026 · Conference Paper
Computational Analysis of Steady State Aerodynamics of Transonic Truss-Braced Wing Configuration in Deep Stall
This study presents a computational investigation of steady state aerodynamics of the Subsonic Ultra-Green Aircraft Research (SUGAR) Transonic Truss-Braced Wing (TTBW) configuration over a wide range …
- arXiv 2023 · arXiv preprint
Automating Bird Diverter Installation through Multi-Aerial Robots and Signal Temporal Logic Specifications
This paper tackles the task assignment and trajectory generation problem for bird diverter installation using a fleet of multi-rotors.
- arXiv 2023 · arXiv preprint
Variation of Critical Crystallization Pressure for the Formation of Square Ice in Graphene Nanocapillaries
Two-dimensional square ice in graphene nanocapillaries at room temperature is a fascinating phenomenon and has been confirmed experimentally.
- arXiv 2023 · arXiv preprint
Polycrystallinity enhances stress build-up around ice
Damage caused by freezing wet, porous materials is a widespread problem, but is hard to predict or control. Here, we show that polycrystallinity makes a great difference to the stress build-up process…
- arXiv 2022 · arXiv preprint
Enhanced Prediction of Three-dimensional Finite Iced Wing Separated Flow Near Stall
Icing on three-dimensional wings causes severe flow separation near stall. Standard improved delayed detached eddy simulation (IDDES) is unable to correctly predict the separating reattaching flow due…
- Embry-Riddle Scholarly Commons 2021 · Journal article (JAAER)
Analysis on the Negative Emotional, Physiological, and Cognitive Responses Elicited from of the Activation of a Stall Alarm
Failing to identify an aerodynamic stall can lead to the inability of an aircraft to sustain flight. To warn pilots of an impending or fully-developed stall, many aircraft have safety devices installe…
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