Which condition requires the APU to have no time limit in amber?

The condition that requires the Auxiliary Power Unit (APU) to have no time limit in amber during both ground and in-flight operations relates to the operational flexibility and reliability of the APU in various scenarios. When the APU is indicated in amber with no time limit, it signifies that it can be used continuously under specific conditions, without the restrictions typically associated with its operation.

In-flight, the APU serves critical functions, such as providing electrical power and bleed air for air conditioning or engine starting, especially during emergencies or abnormal situations. It ensures that aircraft systems remain operational and can support the crew's needs effectively.

Ground operations similarly necessitate that the APU can run as long as required without the constraint of a time limit in amber. This flexibility is essential for powering systems when the main engines are not running, enabling various pre-flight checks, servicing, or during ground delays.

The inclusion of both ground and in-flight conditions under this requirement highlights the importance of the APU functioning effectively across all phases of flight and operational scenarios, ensuring the safety and performance needs of the aircraft are met without unnecessary limitations.