What does an amber PTU indication signify?

An amber PTU indication signifies that the Power Transfer Unit (PTU) is not operational. When the PTU is switched off, the system generates an amber alert to notify the crew of its status. This is crucial information for the pilots, as the PTU plays an essential role in maintaining hydraulic pressure and ensuring system redundancy between the yellow and green hydraulic systems.

When the PTU is turned off, either intentionally or due to a fault, it cannot assist in transferring hydraulic power, which can impact the aircraft's handling and systems relying on hydraulic pressure. Therefore, the amber indication serves as a warning to the flight crew that they need to be aware of the aircraft’s hydraulic situation, allowing them to take appropriate action, if necessary.

In contrast, other indications regarding the PTU's function—like supplying the green or yellow systems—would not result in an amber alert, as providing hydraulic power indicates normal operational status. An overheat condition would typically generate a different warning, specifically pertaining to temperature rather than operational status.