About Me


Send Email


Back to Resource Topics

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
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

I should have called this section mechanics vs engineers. That is the way it seems at times. Both have there roles, I would not ask an engineer to time a magneto nor would I ask a mechanic to determine loads in a shear panel. That being said I do feel that the engineering side is much more of a mystery to the general public. Maybe that is why the resentment of many mechanics towards engineers. A good mechanic is a very creative trouble shooter and problem solver relying on experience and knowledge when it comes to designing. An engineer tends to be less creative but more analytical and is trained to rely on sound engineering principles. Unfortunately neither approach works on its own. Design without analysis to ensure structural soundness is just as poor as a good analysis of a bad design. Unfortunately, at times individuals on both sides have been blind to this. It is interesting though, from my experience more mechanics consider themselves as better designers that engineers.

Here are the general differences in training requirements for the AME and the professional engineer (P.Eng). Having been through both they are both very different with very little overlap.

2 yr Technical Diploma
4 yr University Degree
Work Experience
2 yrs
4 yrs
Technical Exams
Professional Practice Exam

Good design is a multi-disciplined skill that relies on both practical experience and theoretical knowledge. Consider some of the aspects that have to be considered during an aeronautical design change requiring a design change approval:

  • Fit, form and function. Making the installation functional while attained to all the infinite design details. The Designer
  • Certification, regulations, paperwork and more paper work ensuring the design “complies” with the pertinent certification requirements. The DAR or DAO
  • Analysis and substantiation data to support certification effort. The Engineer
  • Drawings to document the installation. The Draftsman
  • Physical installation. The Mechanic
  • The maintenance release ensuring “conformity” with approved data. The AME

Is it possible to do this and be cost effective? Sure, especially for simply design changes. This does not have to be complex but it does have to be considered.

I find myself in an interesting position being an AME and an Engineer, I have the possibility of providing the approval, performing the installation and completing the maintenance release. I have chosen not to do this or provide this service. Ethically, I feel that “compliance” and “conformity” should be preformed by separate individuals.

Whose responsibility is the aircraft modification
Change Product Rule and the basis of certification