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Modification of Canadian Aircraft

What is a design change
The maintenance release for a modification design change
The AC 43.13 as specified data for major modifications

AC 43.13-1B Change 1 Acceptable Methods, Techniques and Practices - Aircraft Inspection and Repair
AC 43.13-2A Acceptable Methods, Techniques and Practices - Aircraft Alterations

Depending on the individual, the FAA Advisory Circulars AC 43.13-1 and -2 can be your best friend or worst nightmare. The reason is because of its vagueness. These documents contain a good collection of information and general practices that a good mechanic should be aware of. Because of this, these documents tend to be more of a collection of good design practices rather than a collection of specific design changes. That means comfort level. What one individual that would have no hesitation in signing off as a modification or repair as in accordance to the AC 43.13 another may argue the point depending on an the individuals experiences. I must admit that I have signed out my share of gray aera design alterations in accordance with the AC 43.13. Personally, I think that the AC 43.13 does fill a needed gap for the mechanic in the day to day performance of his or her work, particularly in the area of older light aircraft where maintenance manuals are lacking and SRMs are non-existent. The best guide I can offer for the use of the AC 43.13 comes from CAR 571.06 as follows, and is also repeated in a similar fashion in the AC 43.13-1:

FAA Advisory Circulars AC 43.13-1 and AC 43.13-2, subject to the following conditions:

(i) the aircraft is a small aircraft, and the alteration does not affect dynamic components, rotor blades, structure that is subject to pressurization loads, or the primary structure of a rotorcraft;

(ii) the alteration does not affect an existing limitation (including the information contained on mandatory placards) or change any data contained in the approved sections of the Aircraft Flight Manual, or equivalent;

(iii) the data are appropriate to the product being altered, and are directly applicable to the alteration being made; and,

(iv) the data are not contrary to the aircraft manufacturer’s data.

Be aware of item 1, the AC 43.13-1 and -2 is only intended for small non-pressurized aircraft. Note that this means that certain sections of AC 43.13-2 that refer to installations on pressurized aircraft can not be used as specified data in the sign off for a major modification or repair in Canada.

Approved data for major modifications
How do you obtain a design change approval
What is a DAR and a DAO
Why use a DAR or DAO
Standards and Approvals
Mechanics, Engineers and good design
Whose responsibility is the aircraft modification
Change Product Rule and the basis of certification