Major Repair / Major Alterations

Major Alteration: An alteration not listed in the aircraft, aircraft engine, or propeller specifications, that:
1) Might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness or
2) Is not done according to accepted practices or cannot be done by elementary operations.
Major Repair: A repair that fits one or more of the following:
1) Might appreciably affect airworthiness by changing weight, balance, structural strength, performance, powerplant operation, or flight characteristics if improperly done or
2) Is not done according to accepted practices or cannot be done by elementary operations.

A primary responsibility of the holder of an IA(Inspection Authorization) is to determine airworthiness by inspecting repairs or alterations for conformity to approved data, and assuring that the aircraft is in a condition for safe operation. During inspection of major repairs or major alterations, the holder of an IA must also determine that they are compatible with previous repairs and alterations that have been made to the aircraft. The holder of an IA must personally perform the inspection. The Federal Aviation Regulations do not provide for delegation of this responsibility.
The approval action should consist of a detailed investigation to establish, at least that:
1. All replacement parts installed conform to approved design and/or have traceability to the original equipment manufacturer (OEM).
2. As installed, the installation conforms to approved data that is applicable to the installation.
3. Workmanship meets the requirements of 14 CFR section 43.13 (the aircraft or product is equal to its original or properly altered condition).                                      4. The data used is appropriate to the aircraft certification rule (e.g. CAR 3, 14 CFR part 23, 25, 27).
5. Work is complete and compatible with other structures or systems. The holder of an IA CANNOT approve the DATA for major repairs or major alterations. They may, however, inspect to see that alterations conform to data previously approved by the FAA (14 CFR section 65.95). This means the holder of an IA must assure that approved data is available and is used as a basis for the approval. This availability determination should be made prior to beginning the repair or alteration. If data is unavailable, or if the holder of an IA is unsure of the acceptability of the available data, the local FAA Airworthiness Inspector should be consulted.
The FAA Inspector may, as the circumstances warrant, be able to:
1. Establish an acceptable basis for approval,
2. Approve the data, or
3. Recommend application for a supplemental type certificate(STC).                   Quite often major repairs are performed that are eventually covered by fabric, metal skin, or another structure. When this situation exists, the holder of an IA should have a clear understanding with the mechanic performing the repair that a precover inspection is necessary. The inspection should assure that the repair was made in accordance with acceptable methods, techniques, and practices prescribed by FAR 43 and the structure to be covered is free from defects, corrosion, or wood rot, and is protected from the elements. In addition, the holder of an IA should inspect other affected areas for hidden damage, if the aircraft has been involved in an accident or incident.                                                                 A log entry is required in the maintenance records and FAA Form 337   "Major Repair and Alteration", must be completed. Minor deviation from approved data is permissible if the change is one that could be approved as a minor alteration when considered by itself. All deviations must be listed on FAA Form 337 and the maintenance record entry when completing the aircraft records. When in doubt, contact the local FAA Inspector who may decide the change is not minor and would need specific approval or amendment of the original approval.

Approved data to be used for major repairs and major alterations may be one or more of the following:
1. Type Certificate Data Sheets.
2. Aircraft Specifications.
3. Supplemental Type Certificates (STC´s), provided it specifically applies to the item being repaired/altered. Such data may be used in whole or part as included within the design data associated with the STC.
4. Airworthiness Directives (AD's)
5. Manufacturer's FAA Approved Data (DOA).
6. Designated Engineering Representative (DER) Approved Data with FAA Form 8110 -3, Statement of Compliance.
7. Designated Alteration Station (DAS) Approved Data.
8. Appliance Manufacturer's Manuals (Excluding Installation Instructions).
9. AC 43.13-1B, Acceptable Methods, Techniques, and Practices (Aircraft Inspection and Repair), may be used directly as approved data without further approval only when there is no manufacturer repair or maintenance instructions that address the repair and the user has determined that it is:
1. appropriate to the product being repaired,
2. directly applicable to the repair being made, and
3. not contrary to manufacturer's data. This data may also be used as a basis to gain FAA data approval for major repairs.                                                                        10. AC 43.13-2B, Acceptable Methods, Techniques, and Practices (Aircraft Alterations), may be used directly as approved data without further approval only when there is no manufacturer alteration instructions that address the modification and the user has determined that it is:
1. appropriate to the product being altered,
2. directly applicable to the alteration being made, and
3. not contrary to manufacturer's data. This data may also be used as a basis to gain FAA data approval for major alterations.
11. FAA Field Approval (FAA Form 337) issued for duplication of identical aircraft may be used as approved data only when the identical alteration is performed on an aircraft of identical make, model, and series by the original modifier. FAA Form 337’s approved in 1955 or earlier may be used as approved data.
12. FAA approved portions of Structural Repair Manuals (SRM).
13. Data in the form of an Appliance Type Approval issued by the Minister of Transport Canada for those parts or appliances for which there is no current Technical Standard Order (TSO) available.
14. Foreign bulletins, for use on US certificated foreign aircraft, when approved by the foreign civil aviation authority.

AC 43.9-1F : Instructions for Completion of FAA Form 337.