Which staff must remain onboard at all times when passengers are present?

The correct response indicates that the flight attendant complement must remain onboard at all times when passengers are present. This requirement is rooted in safety and regulatory standards set by aviation authorities. Flight attendants are specifically trained to handle emergency situations, provide safety instructions, and ensure that passengers are secure throughout the flight. They play a critical role in passenger care and safety, especially during boarding and deplaning, when potential hazards may arise.

In contrast, the roles of ground crew, flight engineers, and maintenance personnel do not involve direct interaction with passengers during flights. Ground crew typically operates in areas such as baggage handling or aircraft servicing and are not required to remain onboard. Flight engineers are primarily focused on the operation of the aircraft during flight and are generally not present when passengers are boarding or deplaning. Maintenance personnel handle aircraft repairs and inspections, which are performed prior to or after passenger operations and do not necessitate their presence onboard while passengers are aboard. Thus, the specific duties and training of flight attendants establish their pivotal role in ensuring passenger safety and well-being, justifying the requirement for their presence at all times when passengers are onboard.