How is flutter testing conducted and what are the clearance criteria?

Flutter flight test process: Ground vibration test (GVT) establishes modal frequencies and shapes for model correlation, Initial analysis predicts flutter boundaries, Flight test proceeds in incremental speed/altitude steps (typically 5-10 knot increments), Excitation provided by control surface pulses, atmospheric turbulence, or oscillators, Frequency and damping extracted from response using PSD, ARMA, or system ID methods, Damping trend monitored (minimum 3% at 1.15 VD or 1.15 MD whichever is more critical per FAR 25.629). Clearance requires positive damping trend to VD/MD with margin. Test abort if unexpected mode or decreasing damping observed. Risk managed through envelope expansion procedures and real-time monitoring. Analysis must cover all fuel states, store configurations, and failure cases.