What condition prohibits the use of wing and/or cowl anti-ice while the APU is used as a bleed source?

The correct choice addresses a critical operational limitation regarding the use of anti-ice systems when the APU (Auxiliary Power Unit) serves as a bleed air source. In manual mode, the system does not automatically control or adjust the bleed air flow, which can lead to potential overheating or insufficient bleed air pressure when engaging the anti-ice systems. This situation can compromise engine performance and safety by failing to adequately manage the engine temperature or initiating unnecessary engine wear if the anti-ice is applied without sufficient bleed air support.

Understanding the implications of using the APU in manual mode is essential for safe aircraft operations, as it emphasizes the importance of ensuring that adequate bleed air and pressure are available before deploying anti-ice systems. The conditions related to in-flight, on the ground, and during taxi operations do not present the same restriction as manual mode usage does, making this limitation specific to that operational setting.