Is frost acceptable on the APU inlet screen?

Frost on the APU (Auxiliary Power Unit) inlet screen is not acceptable because it can block airflow, which is critical for the APU's operation. An unobstructed flow of air is necessary for the APU to function efficiently and effectively; any obstruction can lead to inadequate cooling, overheating, or potential damage to the unit.

Additionally, the presence of frost may indicate that the conditions are not favorable for starting the APU, which could complicate ground operations or lead to further maintenance issues. Therefore, ensuring the inlet screen is free from any frost or ice is essential for the safety and functionality of the aircraft.

This understanding leads to the conclusion that the correct response is that frost is indeed not acceptable on the APU inlet screen.