A gas turbine engine is disclosed having an air injection system useful to supply a relatively pressurized air to a flow path of a compressor. The air injection system includes a port cover operable to open and close a port through which the air can flow to the compressor from a relatively pressurized source. The port cover extends circumferentially around the gas turbine engine and can include a portion that is anchored and an opposite portion coupled to an actuator. Movement of the actuator causes the port cover to open and close the port. Biasing members can be used to urge the port cover into one of an open and closed position against the movement of the actuator.