What is the purpose of the power transfer unit in a 737-800?

The power transfer unit (PTU) in a 737-800 plays a vital role in enhancing the hydraulic system's capabilities, particularly in supporting systems that require a significant amount of hydraulic fluid. Its primary purpose is to ensure that there is an adequate supply of hydraulic pressure for the operation of critical components such as auto-slats and leading-edge flaps.

These systems rely on hydraulic power to function effectively, especially during critical phases of flight like takeoff and landing. The PTU transfers hydraulic fluid between systems to ensure that if one hydraulic system is underutilized, its excess fluid can be used to support another system that might be operating at a higher demand. This balancing act is essential for maintaining aircraft performance and safety.

Other options, although related to aircraft operations, do not align with the specific functionality of the PTU. The supply of fuel to the engines, maintenance of cabin pressure, and control of air conditioning systems are managed by entirely different systems and components designed for those specific purposes. Hence, the role of the PTU is crucial in the context of hydraulic power management, particularly for flight control surfaces like auto-slats and leading-edge flaps.