A gas turbine engine includes a fan section that has a fan. A fan casing surrounds the fan section. A compressor section defines an engine axis. A gear train reduces a rotational speed of the fan relative to a shaft. A low pressure turbine is coupled to the shaft. A nacelle extends along the engine axis and surrounds the fan casing, a bypass ratio of greater than 10. A variable area fan nozzle defines a discharge airflow area. A flutter sensing system includes a controller programmed to move the variable area fan nozzle to vary the discharge airflow area in response to detecting an airfoil flutter condition associated with adjacent airfoils of the fan.