The auxiliary power unit APU is located in the unpressurized tail cone. It is a self-contained unit which can make the aircraft independent of external, pneumatic and electrical power sources. The APU may be started using electrical power supplied by only the aircraft batteries or only the external power source or the engine generator source. The APU provides AC electrical power for the aircraft electrical system and bleed air for engine start and or air conditioning. The APU has an electrically operated air intake flap which when it is opened brings external air to its compressor inlet. Now we will see how information is presented to the pilots. In the cockpit you can check the following APU pyramidders on the ECAM APU page. EGT and compressor speed APU generator APU bleed and air intake flap position. Let's see the different controls that the pilots use to operate the APU. These controls are installed in various places on the overhead panel. The APU master switch and the start push button are installed on the APU control panel. The APU Gen push button switch is located on the electrical panel and is used to control the APU generator. The APU bleed push button switch is located on the air conditioning panel and controls the APU bleed system. During the APU start sequence at approximately 95% and speed, the APU avail memo is displayed on the engine warning display. This is to indicate that the APU perimeters are normal and the APU is available to supply electrical power and bleed air. Note the avail indication also appears in green on the ECAM APU page. On the start push button the on light goes off and the green avail light comes on. As soon as the APU bleed push button switch is set to on, the green APU bleed memo replaces the APU avail memo on the engine warning display. This is to indicate that the APU bleed valve is open with bleed air pressure available. APU fire controls are installed on the fire panel. For additional information refer to the ATA26 fire protection chapter. There is also an APU should off push button and an associated APU fire warning light located on the external power panel refer to the ATA26 fire protection chapter. This panel is located in front of the nose gear bay. The APU parameters are monitored by an electronic control box, ECB which in turn controls the start, the operation and the shutdown of the APU. The ECB initiates a normal shutdown when the master switch is set to off. Note, according to the version an APU cooldown period may be initiated after the closure of the APU bleed valve. The ECB initiates an auto shutdown when a monitored parameter is out of limits. For instance, a slow acceleration during start or a fire has been detected on ground only. Note, the APU will stop immediately. The air intake flap will close 15 minutes after the APU speed is below 7% or after lift-off, if the auto shutdown occurred before take off. The ECB initiates an emergency shutdown when an APU fire push button is pushed on an APU fire panel or an APU shut off push button is used on external power panel. Note, the APU will stop immediately. What is that? In both cases of shutdown, the ECM action is to set the master switch to off. In order to switch off the fault light and to de-energize the ECB.