What must the documents show if an aircraft operation in flight was substantially affected by alteration or repair?

For an aircraft that has undergone alteration or repair and where this work has substantially affected its operation during flight, it is crucial that the aircraft is test-flown and approved for return to service. This is essential to ensure that the alterations or repairs made have been properly verified to be safe and that the aircraft can function as intended.

Test flights allow for comprehensive checks to confirm that all systems are operational, and any modifications carry no detrimental effects on the aircraft's performance and safety. Documentation of this test flight is a regulatory requirement, reflecting compliance with airworthiness standards. This process helps ensure the safety of both the aircraft and its occupants before it is allowed to resume normal operations.

Other options might not satisfy these safety and regulatory standards. For instance, flying with passengers before proper testing could pose significant safety risks, and documentation without subsequent approvals does not lead to regulatory compliance. An inspection by a non-rated pilot does not meet the criteria for ensuring the aircraft's airworthiness after substantial alterations or repairs.