Final answer:
A record must be made of major repair to an aircraft structure in the form of an Airworthiness Directive (AD) or a Service Bulletin (SB).
Step-by-step explanation:
When a major repair is made to an aircraft structure, a record must be made in the form of an Airworthiness Directive (AD) or a Service Bulletin (SB).
An Airworthiness Directive is issued by the Federal Aviation Administration (FAA) and requires the repair to be documented in the aircraft's maintenance records. It is mandatory compliance.
A Service Bulletin, on the other hand, is issued by the aircraft manufacturer to recommend or require a repair. Compliance with a Service Bulletin is usually voluntary unless it is made mandatory by the FAA.