General Authority of Civil Aviation (GACA) Aeronautical Information Publication (AIP) Practice Exam

What happens to the APU when both AC power and left tank DC fuel pump is non-operational?

1. The APU will operate normally

2. The APU will not start

3. The APU will provide emergency power

4. The APU will only operate at full capacity

The correct answer is: The APU will not start

When both AC power and the left tank DC fuel pump are non-operational, the APU (Auxiliary Power Unit) will not start. This is because the APU requires a reliable source of fuel supply and power to function. The left tank DC fuel pump is essential for providing the necessary fuel to the APU. Without the ability to pump fuel from the tank, the APU cannot obtain the fuel it needs for proper operation. Additionally, the lack of AC power further complicates the situation since it typically provides the electrical support for starting the APU and powering its ignition system. Therefore, with both systems inoperative, the conditions necessary for the APU to start and operate efficiently are not met. In contrast, the other options suggest scenarios that are not feasible under these circumstances. The APU cannot provide emergency power or operate at full capacity without fuel and power, nor can it operate normally when these key systems are down.