Final answer:
The amber FAULT light in the APU BLEED pb indicates a malfunction in the aircraft's APU bleed air system, which requires immediate attention.
Step-by-step explanation:
The amber FAULT light in the APU BLEED push-button (pb) is an indicator found in the cockpit of an aircraft. When this light illuminates, it indicates a malfunction within the Auxiliary Power Unit (APU) bleed air system. The APU provides pneumatic power for air conditioning and electrical power for various systems when the main engines are not running, especially on the ground. An illuminated FAULT light suggests that the bleed air has either overheated, there is excessive pressure, or there could be another system-related issue, signaling to the pilot or maintenance crew that immediate attention is required.