A method of operating a gas turbine engine of an aircraft, the gas turbine engine comprising a compressed air switching system having a switching valve, the method comprising: operating the gas turbine engine in one of a powered mode and a standby mode, wherein when the gas turbine engine is operating in the powered mode bleeding air via the compressed air switching system to a plurality of parts of the gas turbine engine from a first bleed location of a compressor section of the gas turbine engine, and when the gas turbine engine is operating in the standby mode bleeding air via the compressed air switching system from a second bleed location that is downstream of the first bleed location relative to air flow through the compressor section; determining a temperature in a main gas path of the gas turbine engine at a location at or downstream of a combustor of the gas turbine engine and then actuating the switching valve of the compressed air switching system to bleed air from the other one of the first and second bleed locations; determining the temperature of the gas turbine engine after the step of actuating the switching valve; and in response to determining that a difference between the temperatures before and after the step of actuating the switching valve meets a threshold, executing at least one of a first action with respect to at least one of the gas turbine engine and the switching valve, and executing a second action with respect to the at least one of the gas turbine engine and the switching valve, the second action being different from the first action, wherein when the gas turbine engine is operating in the powered mode, the first action includes one of switching the gas turbine engine to the standby mode in response to a command from an operator of the aircraft to switch the gas turbine engine to the standby mode, and allowing a switch of the gas turbine engine to the standby mode in response to the command, wherein when the gas turbine engine is operating in the powered mode, the second action includes preventing the gas turbine engine from switching to the standby mode in response to the command. operating the gas turbine engine in one of a powered mode and a standby mode, wherein when the gas turbine engine is operating in the powered mode bleeding air via the compressed air switching system to a plurality of parts of the gas turbine engine from a first bleed location of a compressor section of the gas turbine engine, and when the gas turbine engine is operating in the standby mode bleeding air via the compressed air switching system from a second bleed location that is downstream of the first bleed location relative to air flow through the compressor section; determining a temperature in a main gas path of the gas turbine engine at a location at or downstream of a combustor of the gas turbine engine and then actuating the switching valve of the compressed air switching system to bleed air from the other one of the first and second bleed locations; determining the temperature of the gas turbine engine after the step of actuating the switching valve; and in response to determining that a difference between the temperatures before and after the step of actuating the switching valve meets a threshold, executing at least one of a first action with respect to at least one of the gas turbine engine and the switching valve, and executing a second action with respect to the at least one of the gas turbine engine and the switching valve, the second action being different from the first action, wherein when the gas turbine engine is operating in the powered mode, the first action includes one of switching the gas turbine engine to the standby mode in response to a command from an operator of the aircraft to switch the gas turbine engine to the standby mode, and allowing a switch of the gas turbine engine to the standby mode in response to the command, wherein when the gas turbine engine is operating in the powered mode, the second action includes preventing the gas turbine engine from switching to the standby mode in response to the command.