NTSB CAROL · Event
Event ATL91FA013
Aircraft involved
Probable cause & findings
THE ACCIDENT WAS INADEQUATE MAINTENANCE OF THE HELICOPTER, ALLOWING A TAIL ROTOR DRIVE SHAFT BEARING TO EXCEED WEAR LIMITS. THIS RESULTED IN HIGH LOADS ON THE TAIL ROTOR DRIVE SHAFT, AND THE RESULTING FATIGUE FAILURE OF THE DRIVE SHAFT.
Factual narrative
THE TWO PASSENGERS REPORTED THAT THEY HEARD A 'POP' SOUND, FOLLOWED BY THE HELICOPTER STARTING A CLOCKWISE SPIN TO THE RIGHT. THE HELICOPTER DESCENDED INTO THE TREES ON THE SIDE OF A STEEP SLOPE. INVESTIGATION REVEALED THAT THE TAIL ROTOR DRIVE SHAFT FAILED IMMEDIATELY FORWARD OF THE TAILBOOM EXTENSION TUBE. THE DRIVE SHAFT FAILED FROM FATIGUE CRACKING, PROPAGATING AT A HIGH RATE, SUGGESTING HIGH LOADS. THE T/R DRIVE SHAFT FORWARD BEARING HOUSING OUTER DIAMETER DIMENSION AND THE INNER DIAMETER OF THE TAILBOOM EXTENSION TUBE WERE WORN BEYOND REPLACEMENT LIMITS AND SHOULD HAVE BEEN REPLACED ACCORDING TO THE BELL MAINTENANCE AND OVERHAUL MANUAL. THE PASSENGER THREE-PLACE BENCH SEAT HAD BEEN ALTERED SO THAT THE INDIVIDUAL SEAT BELTS HAD BEEN MODIFIED INTO ONE SINGLE LONG BELT. THE BELT COULD BE OPENED ONLY ON THE LEFT SIDE OF THE BELT; THE BUCKLE ON THE RIGHT SIDE OF THE BELT WAS TAPED CLOSED WITH SILVER DUCT TAPE. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12
Verbatim from NTSB's published report. Source file
NTSB_1990_ATL91FA013.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 (maintenance). Sourced from NASA NTRS, NTSB Safety Studies, FAA CAMI, AOPA Air Safety Institute, Embry-Riddle Scholarly Commons, arXiv, and the Semantic Scholar academic graph.
- Embry-Riddle Scholarly Commons 2026 · Journal article (IJAAA)
From Reactive to Predictive: A hybrid Trust-Mediated Adoption Framework for Data-Driven Maintenance in Distributed-Authority Aviation Environments
Modern aviation maintenance operates within increasingly data-intensive technological environments, yet the operational integration of predictive maintenance into routine decision-making remains incon…
- Semantic Scholar 2025 · Article (Applied Sciences)
Decision-Making Framework for Aviation Safety in Predictive Maintenance Strategies
The implementation of predictive maintenance (PM) in aviation presents unique challenges due to strict safety requirements, complex operational environments, and regulatory constraints.
- Embry-Riddle Scholarly Commons 2024 · Journal article (JAAER)
Low-Resource Automatic Speech Recognition Domain Adaptation – A Case-Study in Aviation Maintenance
With timeliness and efficiency being critical in the aviation maintenance industry, the need has been growing for smart technological solutions that optimize and streamline the different underlying ta…
- Embry-Riddle Scholarly Commons 2024 · Journal article (JAAER)
A New Trajectory in UAV Safety: Leveraging Reinforcement Learning for Distance Maintenance Under Wind Variations
In the field of aviation, safety is a critical cornerstone, and the operation of Unmanned Aerial Vehicle (UAV) systems is deeply connected with this principle.
- Embry-Riddle Scholarly Commons 2024 · Journal article (IJAAA)
Just Culture in Aviation: A Metaphorical Study on Aircraft Maintenance Students
Just Culture, a sub-dimension of safety culture, has been a prominent and debated topic in aviation safety in recent years.
- Embry-Riddle Scholarly Commons 2024 · Journal article (IJAAA)
Performance PRISM: A Comprehensive Framework For Performance Measurement In Aircraft Maintenance
Aircraft maintenance is governed by rigorous safety requirements and high operational complexity, demanding robust performance measurement frameworks to ensure optimal maintenance practices.
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