Under what condition can a ramp check occur without the crew present?

The correct rationale for allowing customs to inspect without crew presence is based on the specific regulations surrounding customs authorities and their responsibilities during ramp checks. Customs agents have the authority to conduct inspections when an aircraft arrives from or is departing to a foreign location. This inspection does not necessarily require the crew to be present, as customs processes often involve checking documentation and compliance with immigration and customs regulations, which can be handled independently of the crew's direct involvement.

The situation differs from other options where various limitations and conditions apply. For instance, inspections by maintenance personnel would typically require the crew's presence to ensure safety protocols and clarify operational procedures. Similarly, ramp checks by other entities, such as FAA inspectors, generally expect crew presence unless there is a specific regulatory allowance or circumstance.