T/F: there’s NO on/off switch on CAP units; they're always on if engine is on.

T/F: there’s NO on/off switch on CAP units; they're always on if engine is on.

• A. False
• B. CAP units can be powered off
• C. CAP is powered independently of engine
• D. True

Answer: (D)

In the 787, cabin air packs are part of an automated environmental control system. There isn’t a manual on/off switch for each CAP unit; their operation is controlled by the Pack Control Unit and coordinated with engine power and system demand. When the engines are running and electrical power is available, the ECS automatically commands the CAPs to provide conditioned air to the cabin. If power is removed or a fault isolates the packs, they won’t operate. So, yes—the CAP units don’t have a dedicated on/off switch and function whenever the engines are providing power, which is why the statement is correct.

In the 787, cabin air packs are part of an automated environmental control system. There isn’t a manual on/off switch for each CAP unit; their operation is controlled by the Pack Control Unit and coordinated with engine power and system demand. When the engines are running and electrical power is available, the ECS automatically commands the CAPs to provide conditioned air to the cabin. If power is removed or a fault isolates the packs, they won’t operate. So, yes—the CAP units don’t have a dedicated on/off switch and function whenever the engines are providing power, which is why the statement is correct.