Should the engines' bleed and apu bleed valves be in operation at the same time? For example, during pushback, the apu is operational and its bleed valve is open, however, so are the engine bleed valves. Should these be opened only after engine start, in order to prevent a dual bleed warning?The same applies for taxiing in when the apu is operational. Whilst taxiing in, can the engine bleed valves be turned off shortly before engine shutdown to prevent a dual bleed warning?I'd appreciate it if someone could clarify the operation of the bleed valves during engine start and shutdown, and when the apu is operational.Thanks. :)

Engine bleed switches are normally always on (also when engines are shut down!). So when APU is running (with apu bleed on) and the engines are running, you will get the dual bleed warning. After engine start, switch off the APU/APU bleed air and the message will disappear.Do not use more than idle thrust when the dual bleed light is illuminated.