The Boeing 757’s pneumatic system regulates air for various crucial functions, such as air conditioning, engine starting, and ice protection, utilizing air from engines, the APU, or ground carts. The system’s user interfaces include the Total Air Temperature (TAT) probe, hydraulic reservoir pressurization, and water tank pressurization. Pressurised air is bled from two ports on the engine compressor section, managed to ensure appropriate pressure and temperature for distribution to user systems.
The APU provides bleed air on the ground and can serve as a backup in-flight below 17,500 feet in case of engine failure or malfunction. For on-ground support, a pneumatic ground cart can supply air when the aircraft is parked.
The system distributes air through ducts to user systems, with pressure monitored by duct pressure transducers. Interfaces with the engine bleed configuration cards (EBCC) allow signals from these cards to the Thrust Management Computer (TMC), Electronic Engine Control (EEC), and the Flight Management Computer (FMC).
Control panels on the overhead P5 panel provide indications and controls for the pneumatic system. The EBCCs, located in the main equipment center, relay signals from the PRSOVs to various user systems, ensuring communication between the pneumatic system and other aircraft systems.
The APU bleed air system supplies compressed air primarily to the left side of the air distribution system and can extend to the right when the isolation valve is open. The distribution system itself, made from materials like titanium, has an isolation valve dividing it into left and right sides, each with various interfaces for engine air supply, air conditioning packs, and ice protection systems.
The system’s indicating components provide data to the pneumatics control panel and EICAS, including valve positions, air pressure and temperature, and fault indications like overpressure and overtemperature. These conditions are reflected on the control panel and EICAS, with specific lights indicating different fault conditions such as closed PRSOVs with engines running, APU shutoff valve misalignment, or overheat and overpressure in the engine air supply system.