Gas turbine with a secondary air system and method for operating such a gas turbine

The gas turbine (10) has a compressor (12), a combustion chamber (14) for producing one hot gas, a turbine (16) with multiple turbine blade rings and an air system (24). A regulating unit (V21) is provided in a coolant passage (S1), by which a cooling air outlet (E2) is connected with a cooling air opening (M1) in place of another cooling air outlet (E1). An independent claim is also included for a method for operating a gas turbine.