What must occur if an aircraft's operation has been substantially affected by an alteration or repair?

When an aircraft undergoes an alteration or repair that substantially affects its operation, it is essential that the aircraft be test flown and approved for return to service. This process ensures that any changes made do not negatively impact the aircraft's performance, safety, or compliance with regulatory standards.

Testing the aircraft after such modifications allows for the assessment of its flight characteristics and systems functionality in real-world conditions, confirming that it operates safely and meets all operational specifications. The approval for return to service is significant because it provides assurance to the pilot, maintenance personnel, and any subsequent users that the repairs or alterations have been appropriately evaluated and that the aircraft is fit for flight.

In contrast, while inspections by designated personnel and grounding for a specific duration are parts of maintenance protocols, they alone do not substitute for the critical step of testing and ensuring that the aircraft is safe for operation following significant changes. A complete overhaul may be necessary in some situations but is not universally required after every alteration or repair.