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

What is the maximum pressure altitude for the APU to pack operation?

1. 7000 ft

2. 6900 ft

3. 6500 ft

4. 6000 ft

The correct answer is: 6900 ft

The maximum pressure altitude for APU (Auxiliary Power Unit) pack operation is critical because it defines the operational limits under which the APU can effectively provide the necessary electrical and pneumatic power to support aircraft systems, especially environmental control systems. In this context, option indicating 6900 ft is the maximum operational altitude for the APU packs, which means that at this altitude, the APU can function effectively enough to supply necessary functions like air conditioning and cabin pressurization. This altitude is typically determined by both performance specifications of the APU and safety requirements for maintaining adequate operations. Choosing this specific altitude acknowledges that there are limitations to APU performance based on ambient conditions, which are affected by altitude. Beyond this pressure altitude, the ability of the APU to provide adequate pressure and airflow for pack operations starts to diminish, which may lead to operational concerns, such as overheating or insufficient airflow to maintain cabin comfort and safety. Understanding these limitations is essential for flight crews and maintenance personnel to ensure safe and efficient aircraft operation.