What operational requirement must be observed when ferrying a turbine-engine-powered airplane for engine repair?

The correct answer focuses on the operational requirement that only the required flight crew members may be on board when ferrying a turbine-engine-powered airplane for engine repair. This is primarily a safety and regulatory consideration. By limiting the number of people on board to just those required for the flight, it minimizes risk.

In situations where an aircraft is being ferried for repairs, it is often in a state that may not be fully operational or optimal for passenger safety. Hence, allowing only the essential crew ensures that any emergencies can be managed without the added complexity of passengers on board. This requirement also aligns with guidelines often provided by aviation authorities intended to ensure safety during such operations.

Regarding the other options that mention passengers or weight limits, while these may also have implications in broader operational contexts, they do not specifically address the immediate safety concerns associated with ferrying an aircraft under repair conditions. The daylight requirement, while potentially beneficial, is not a mandated operational regulation in this scenario.