Is it permissible to use the APU bleed and HP cart simultaneously?

Using both the APU bleed and the high-pressure ground air cart (HP cart) simultaneously is prohibited due to potential issues with pressure levels and system integrity. The systems are designed to operate independently, and using them together can lead to complications such as excessive pressure in the pneumatic system, which could damage components or lead to malfunctions.

Operating the APU provides bleed air for starting engines and supplying pneumatic functions, while the HP cart serves a similar purpose but is meant for ground operations. When both are used at the same time, it can create conflicts in the pneumatic system's demands and responses, which is why it's not allowed.

Understanding this distinction is essential for ensuring safe and effective aircraft operation in various scenarios, highlighting the importance of adhering to standard operating procedures to maintain aircraft integrity and performance.