If an aircraft's operation in flight was substantially affected by an alteration or repair, what must be shown regarding the flight prior to its operation?

For an aircraft that has undergone alterations or repairs that could substantially affect its operation in flight, it is essential that the aircraft is test flown and shown to be in a safe and operable condition before being returned to service. This is critical to ensure that any changes made do not adversely impact the aircraft's performance, handling characteristics, or safety.

After significant alterations or repairs, the manufacturer’s guidelines or regulatory requirements typically dictate that a thorough evaluation of the aircraft's performance be conducted under controlled conditions. This test flight is performed to confirm that all systems are functioning as intended and that the aircraft complies with safety standards. Following a successful test flight, documentation and approval for return to service are essential for regulatory compliance and to instill confidence in the aircraft's condition.

The other options do not address the crucial requirement of safety verification through a test flight following repairs or modifications. A student pilot operating the aircraft does not relate to its safe return to service after modifications. Similarly, conducting the flight under VFR conditions, or including passengers, does not ensure that the aircraft has been properly evaluated. Thus, the necessity for a test flight to demonstrate compliance and safety after alterations or repairs is paramount.