Sierra Pattern A320 [extra Quality] Review

Because modern Airbus operations heavily emphasize automation, the Sierra Pattern serves as an essential "raw data" exercise. Pilots must turn off the Flight Director (FD) and Autopilot (AP), relying purely on basic pitch and thrust settings to fly the aircraft. The Anatomy of the Sierra Pattern

This is correct, but there is a trap. Starting the APU draws massive current from the emergency batteries. If you attempt an APU start while also cycling the engine master switches for a windmill restart, you can drain the batteries below 20 volts. At that point, the FADECs and the flight control computers (ELAC/SEC) reboot or fail. sierra pattern a320