Which standard practice is recommended for checking aircraft pneumatic systems?

When checking aircraft pneumatic systems, the recommended standard practice focuses on inspecting for leaks and ensuring that proper pressure levels are maintained. Pneumatic systems rely on the pressurized air to operate various components, and any leaks can lead to a decrease in efficiency, failure of systems, or even unsafe conditions during flight.

Proper pressure levels are crucial because they determine how effectively the pneumatic systems will function. If the pressure is too low, the systems may not operate correctly, which could adversely affect the aircraft's performance and safety. Monitoring these aspects ensures the reliability and functionality of the pneumatic system, making it a fundamental practice in aircraft maintenance.

Other options, while relevant to different systems or aspects of aircraft maintenance, do not directly address the critical aspects of pneumatic system checks. Fuel contamination and structural integrity do not pertain specifically to pneumatic systems, and ensuring the smooth rotation of components, while important in mechanical systems, is not the primary concern for pneumatic systems where pressure and leak integrity play a more pivotal role.