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

Under what condition will the L, C and R isolation valves open automatically?

1. When the cabin temperature reaches maximum limits

2. During cross-bleed start

3. When the aircraft is at cruising altitude

4. During emergency descent

The correct answer is: During cross-bleed start

The correct answer is that the L, C, and R isolation valves will open automatically during a cross-bleed start. In aviation, a cross-bleed start involves using the bleed air from one engine to start another engine. This process requires the isolation valves to open in order to facilitate the flow of bleed air between systems, ensuring an effective engine start. If we consider the other scenarios: opening the isolation valves at maximum cabin temperature limits is not typical, as the valves are specifically designed to manage bleed air, not primarily for temperature control. While cruising altitude might require specific flow conditions, it does not trigger the automatic opening of these valves. Lastly, during an emergency descent, the focus shifts to maintaining cabin pressure and ensuring safety, which means that the isolation valves may not be relevant or required to open automatically.