FAR 23.2245 — Aeroelasticity
FAR 23.2245 requires Part 23 airplanes to be free from flutter, control reversal, and divergence across the design envelope. See what it means for pilots.
FAR 23.2245 is an airworthiness standard under Part 23 (small airplanes) that protects against destructive aerodynamic-structural interactions. The airplane must be demonstrated to be free from three dangerous phenomena:
- Flutter — a self-exciting oscillation of a structure (like a wing or tail) caused by airflow.
- Control reversal — when a control surface deflection produces the opposite of the intended response due to structural bending.
- Divergence — a runaway structural deflection that doesn't return to neutral.
These must be ruled out:
- At all speeds within and sufficiently beyond the structural design envelope;
- For any configuration and condition of operation;
- Accounting for critical degrees of freedom; and
- Accounting for any critical failures or malfunctions.
The applicant (manufacturer) must also establish tolerances for every quantity that affects flutter — mass balance of control surfaces, stiffness, damping, etc.
Why it matters operationally: This is why pilots must respect VNE/VMO, keep control surfaces properly balanced after painting or repair, and ensure no loose hardware or play exists in control systems. Exceeding the envelope can trigger flutter that destroys the airframe in seconds.