Final answer:
A FAULT indication in the PTU pb means there is a malfunction in the Power Transfer Unit of an aircraft's hydraulic system, which could be due to loss of pressure, electrical issues, or mechanical failure.
Step-by-step explanation:
When there is a FAULT indication in the PTU pb, which stands for Power Transfer Unit pushbutton, it means there is a detected malfunction within the PTU system. The PTU is an important part of an aircraft's hydraulic system, providing power to actuate various airplane components such as flaps, landing gear, and brakes. A FAULT indication could suggest a variety of issues, such as a loss of hydraulic fluid pressure, an electrical problem, or a mechanical failure. In aviation, addressing any fault indications is crucial for the safety and operability of the aircraft.