The APU START button triggered OPEN FLAP and APU START.

Opening the air intake flap and starting the APU where linked together to only one procedure. When the APU MASTER button was pressed, only indications on the APU page on the SD turned from amber to "active". Nothing more happened. When also the APU START button was pressed, the air intake flap opened and APU start was initiated, as soon as the flap was open.

• How it works now:

The APU MASTER button triggers OPEN FLAP, the APU START button triggers APU START.

Opening the flap and starting the APU are now two separated procedures. When the APU MASTER button is pressed, indications on the APU page on the SD turn from amber to "active" and the air intake flap opens. This takes about 20 seconds, then the green FLAP indication appears. When the APU MASTER button is pressed, which need not be at the same time, APU start is initiated, provided the flap is open.

This is how it works on the real Airbus. So the pilot has the option to open the flap early, even some minutes before APU start. This is of advantage when the taxi time after landing is difficult to predict, since opening the flap does not burn fuel, but it shortens the entire APU start procedure by ~20 seconds. So the APU can be started shortly before reaching the parking position, thereby avoiding unnecessary running time of APU or worse, of main engines.