A gas turbine engine comprising: a fan (42; 214); a nacelle (100; 208) including a flutter damper disposed forward of the fan, the flutter damper comprising: an acoustic liner (101; 216) having a perforated radial inner face sheet and a radial outer back sheet , the acoustic liner being configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter; and a circumferential array of chambers disposed about a nacelle inlet , the circumferential array achieving a desired damping volume, each of the chambers being secured to the radial outer back sheet, being in fluid communication with the acoustic liner, and being configured for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes; wherein: (i) the nacelle and a core cowl form a bypass duct , the bypass duct forming a convergent-divergent fan exit nozzle; and/or (ii) the gas turbine engine includes a variable area fan nozzle , the variable area fan nozzle is capable of being in an opened position and a closed position, wherein the opened position has a larger fan exit area than the closed position; and/or (iii) the fan is a shrouded fan. a fan (42; 214); a nacelle (100; 208) including a flutter damper disposed forward of the fan, the flutter damper comprising: an acoustic liner (101; 216) having a perforated radial inner face sheet and a radial outer back sheet , the acoustic liner being configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter; and a circumferential array of chambers disposed about a nacelle inlet , the circumferential array achieving a desired damping volume, each of the chambers being secured to the radial outer back sheet, being in fluid communication with the acoustic liner, and being configured for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes; an acoustic liner (101; 216) having a perforated radial inner face sheet and a radial outer back sheet , the acoustic liner being configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter; and a circumferential array of chambers disposed about a nacelle inlet , the circumferential array achieving a desired damping volume, each of the chambers being secured to the radial outer back sheet, being in fluid communication with the acoustic liner, and being configured for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes; wherein: (i) the nacelle and a core cowl form a bypass duct , the bypass duct forming a convergent-divergent fan exit nozzle; and/or (ii) the gas turbine engine includes a variable area fan nozzle , the variable area fan nozzle is capable of being in an opened position and a closed position, wherein the opened position has a larger fan exit area than the closed position; and/or (iii) the fan is a shrouded fan. (i) the nacelle and a core cowl form a bypass duct , the bypass duct forming a convergent-divergent fan exit nozzle; and/or (ii) the gas turbine engine includes a variable area fan nozzle , the variable area fan nozzle is capable of being in an opened position and a closed position, wherein the opened position has a larger fan exit area than the closed position; and/or (iii) the fan is a shrouded fan. <EOS>