Although the cause of an airplane accident has never been attributed to properly applied repairs using the original repair data, repairs may be of concern as time-in-service increases for the following reasons:

• As airplanes age, both the number and age of the existing repairs increase.
• Along with this increase is the possibility of unforeseen repair interaction, autogenous failure, or other damage occurring in the repaired area.
• The continued operational safety of these airplanes depends primarily on a satisfactory maintenance program (inspections conducted at the right time, in the right place, using the most appropriate technique).

• To develop this program, a damage-tolerance evaluation of repairs to flight-critical structures is essential.
• The longer an airplane is in service, the more important this evaluation and a subsequent inspection program become.

The damage-tolerance methodology has evolved gradually over the last 20 or more years.

• Some existing repairs described in the airplane manufacturers’ Structural Repair Manuals (SRM) were not designed to current standards.
• Repairs accomplished in accordance with the information contained in the early versions of the SRM’s may require additional inspections if evaluated using the current methodology.
• Because a regulatory requirement for damage-tolerance was not applied to airplane designs type certificated before 1978, the damage-tolerance characteristics of repairs may vary widely and are largely unknown.

(a) FAA shall approve design data in support of major repairs in accordance with:

• FAA Order 8110.4 Type Certification;
• FAA Order 8110.37, Designated Engineering Representative Guidance Handbook; FAA Order 8100.15, Organization Designation Authorization Procedures; and
• FAA Order 8300.16, Major Repair and Alteration Data Approval”.
• Minor repairs are made in accordance with “acceptable” data, in accordance with 14 CFR Part 43.