Airworthiness Concern Highlights Reports of In-Flight Oscillations
May 6, 2025 — The Federal Aviation Administration (FAA) has issued an Airworthiness Concern Sheet (ACS) after receiving multiple reports of severe, uncommanded vertical vibrations during flight in Bell 206L-series helicopters. The issue affects all models in the 206L family—the 206L, 206L-1, 206L-3, and 206L-4, regardless of serial number.
🔍 What's Happening?
Pilots have reported intense, sudden vertical vibrations that appear without warning and leave no clear evidence of mechanical failure after landing. In some cases, vibrations subsided when the pilot increased collective input, suggesting a link to rotor system loading. Low friction in the collective control has also been identified as a possible contributing factor.
In one documented case under NTSB investigation (WPR24LA319), vibration led to tailboom damage, though the aircraft was landed safely.
✈️ FAA Seeks Operator Feedback
The FAA is actively collecting reports from operators who have experienced similar vibration events, whether recent or historical. Information that can aid the investigation includes:
Aircraft Details
- Model (L, L-1, L-3, or L-4)
- STC or PMA parts (e.g., rotor blades, torsion straps)
- Aircraft weight, fuel level, center of gravity
- Number of occupants
- Collective friction setting
Flight Conditions
- Airspeed and altitude
- Flight phase (climb, cruise, descent)
- Wind, turbulence, and other weather factors
Incident Information
- Date and time of event
- Pilot responses and corrective actions
- Post-flight inspection findings (e.g., trim tab loss, structural damage)
Any additional observations that could help pinpoint causes are welcomed by the FAA.
⚙️ What Happens Next?
No Airworthiness Directive (AD) or Special Airworthiness Information Bulletin (SAIB) has been issued yet. The FAA may consider:
- ✔️ Issuing an AD if a safety fix is warranted
- 📝 Publishing a SAIB for broader awareness
- ✅ Concluding no further action is needed
This ACS is part of the FAA’s ongoing collaboration with operators to address airworthiness concerns early and thoroughly.
📢 Who’s Been Notified?
The ACS has been distributed to:
- FAA field offices
- Bell Textron Canada
- Type clubs and certificate holders
- Vertical Aviation International (VAI)
- Air Medical Operator Association (AMOA)
- Airborne Public Safety Association (APSA)
⏱️ Response Deadlines
- Emergency reports: within 10 days
- Alert-level concerns: within 30 days
- General information: within 90 days
📬 Contact the FAA
James Guo
Aviation Safety Engineer, FAA AIR-772
📍 3960 Paramount Blvd, Suite 100, Lakewood, CA 90712
📞 (562) 627-5357
📧 james.guo@faa.gov
🔗 View the full FAA ACS document:
FAA ACS - 206L Series Vertical Vibration (PDF)
