Which power source is used to start the APU?

The Auxiliary Power Unit (APU) on the Dassault Falcon 7X is primarily started using Battery #1. This is significant because the APU is essential for providing electrical power and pneumatic pressure when the main engines are not running.

Using Battery #1 ensures that there is sufficient power to initiate the APU start cycle, as it has the capacity to deliver the necessary voltage and current. The APU then becomes capable of supplying power to the aircraft's systems and can assist in engine starting operations.

While Battery #2 could hypothetically be utilized in certain scenarios, and other power sources such as the Ground Power Unit can provide external electrical power, the standard operational procedure specifies the use of Battery #1 for starting the APU. The emergency power supply is not typically used for routine operations such as starting the APU, reinforcing Battery #1's role in this specific function.