When must the PACK be in operation while on the ground?

The correct choice is based on the need to manage cabin temperatures effectively and to prevent overheating of components during ground operations. The PACK (air conditioning pack) must be operational when the aircraft electrical system is powered on for more than 30 minutes and the outside air temperature (OAT) exceeds 40°C. This requirement helps ensure that the cabin environment remains safe and comfortable for both crew and passengers and prevents equipment from overheating.

When the electrical system is on for an extended period without proper cooling, it can lead to excessive heat buildup in the aircraft, potentially affecting various systems and the overall safety of operations. Therefore, activating the PACK under these specific conditions is essential for maintaining an appropriate temperature and air quality in the aircraft.

Other options, while relevant to aircraft operation scenarios, do not address the critical need to maintain temperature control related to the specified conditions. The necessity for temperature regulation is highlighted specifically in this choice, making it the best answer.