A gas turbine engine comprising: a compressor; a turbine coupled in flow communication with said compressor; a fan bypass duct; an outer casing circumscribing said compressor, said turbine and said fan bypass duct; an augmentor in flow communication with the fan bypass duct; and an annular slide valve assembly defining a passage to channel fan bypass air to said augmentor, said annular slide valve assembly comprising: an annular slide valve; a valve seat positioned such that an airflow passage is defined between said annular slide valve and said valve seat; and a control valve coupled to said annular slide valve and configured to channel compressed air to said slide valve to control the position of the slide valve relative to the valve seat thus regulating a quantity of fan bypass air channeled to said gas turbine engine augmentor; wherein a diffuser is coupled radially inward of said outer casing, said valve seat coupled to said diffuser; and a separation liner is coupled between said outer casing and said diffuser within the bypass duct, said annular slide valve slidably coupled to said separation liner, the annular slide valve assembly further comprising: a first sealing member coupled between said annular slide valve and said separation liner; a second sealing member coupled between said annular slide valve and said separation liner such that a first cavity is defined between said annular slide valve, said separation liner and the first and second sealing members; and a third sealing member coupled between said annular slide valve and said separation liner such that a second cavity is defined between said annular slide valve, said separation liner and the second and third sealing members. a compressor; a turbine coupled in flow communication with said compressor; a fan bypass duct; an outer casing circumscribing said compressor, said turbine and said fan bypass duct; an augmentor in flow communication with the fan bypass duct; and an annular slide valve assembly defining a passage to channel fan bypass air to said augmentor, said annular slide valve assembly comprising: an annular slide valve; a valve seat positioned such that an airflow passage is defined between said annular slide valve and said valve seat; and a control valve coupled to said annular slide valve and configured to channel compressed air to said slide valve to control the position of the slide valve relative to the valve seat thus regulating a quantity of fan bypass air channeled to said gas turbine engine augmentor; wherein a diffuser is coupled radially inward of said outer casing, said valve seat coupled to said diffuser; and a separation liner is coupled between said outer casing and said diffuser within the bypass duct, said annular slide valve slidably coupled to said separation liner, the annular slide valve assembly further comprising: an annular slide valve; a valve seat positioned such that an airflow passage is defined between said annular slide valve and said valve seat; and a control valve coupled to said annular slide valve and configured to channel compressed air to said slide valve to control the position of the slide valve relative to the valve seat thus regulating a quantity of fan bypass air channeled to said gas turbine engine augmentor; wherein a diffuser is coupled radially inward of said outer casing, said valve seat coupled to said diffuser; and a separation liner is coupled between said outer casing and said diffuser within the bypass duct, said annular slide valve slidably coupled to said separation liner, the annular slide valve assembly further comprising: a first sealing member coupled between said annular slide valve and said separation liner; a second sealing member coupled between said annular slide valve and said separation liner such that a first cavity is defined between said annular slide valve, said separation liner and the first and second sealing members; and a third sealing member coupled between said annular slide valve and said separation liner such that a second cavity is defined between said annular slide valve, said separation liner and the second and third sealing members.