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Changes or modifications and repairs to aircraft

Guidance on minor and major changes or repairs

  • Changes (or modifications) to an aircraft, engine or propeller are any change to the approved type design. The change may be physical such as the installation of a new system or replacement of a part for one of a new part number but could also only be a change to documentation such as the Aircraft Flight Manual (AFM) or Operational Suitability Data (OSD).

    Repairs are the result of design activities for the elimination of damage and/or restoration of the aircraft/engine/propeller to an airworthy condition. This could also include the assessment of damage to allow continued operation without physical repair of that damage.

    All changes and repairs need to be CAA approved. The means of approval depends on the classification of the change or repair and whether Design Organisation Approval (DOA) privileges can be used. These pages address the case when the DOA privileges are not used and the change or repair is approved directly by the CAA.

    Changes and Repairs are classified as major or minor.

    A minor change has ‘no appreciable effect’ on airworthiness or environmental characteristics. All other changes are major. The criteria and guidance material for determining the correct classification is in 21.A.91. For repairs there are additional criteria and guidance in 21.A.435.

    Anyone may apply for the approval of a minor change or repair by following the process shown below.

    The Applicant for the approval of a major change or major repair must (usually) hold an appropriate design organisation approval. The process for major change or repair approval is shown below on this page.

    Note: For some classes of light aircraft, the change or repair may not need CAA approval if it has been classified as a Standard Change or Standard Repair and is embodied as per CS-STAN.

  • Minor changes and repairs

    A minor change or repair is one that has 'NO appreciable effect' on airworthiness or environmental characteristics. 
    Modification of data and documentation such as the Aircraft Flight Manual (AFM) and Operational Suitability Data (OSD) will be processed as changes/repairs to the type design. There is no separate application.

    Eligibility

    Anyone may apply for the CAA approval of a minor change or minor repair.

    How to apply

    An application is made using CAA Form SRG1726NR

    Approval process

    Applicant
    responsible
    for    		 CAA
    responsible
    for    		  Activity
    x  

    Submit an application on CAA Form SRG1726NR and provide the initial 'data pack' which should include:

    • Definition of the change, (applicability by product type/model and description)
    • Accomplishment instructions for the embodiment of the change/repair
    • Instructions for Continued Airworthiness
    • Flight Manual Supplement (if applicable)
    • Record of compliance with the applicable (and appropriate) airworthiness, environmental and OSD requirements.

    Further guidance may be found in CAP 1419

    CAP 1419 was originally developed for non- Part 21 changes, but the intent of the guidance within is still applicable for minor changes to Part 21 aircraft.
      x Confirm that the change/repair can be classified as Minor
    x x CAA will review the 'data pack' to check that compliance with the appropriate airworthiness requirements has been demonstrated and/or advise the applicant if any further information is required
      x Confirm that compliance has been demonstrated and issue the Minor Change/repair approval certificate

     

    Major changes / STC and major repairs

    A major change or repair is one that has 'an appreciable effect' on airworthiness or environmental characteristics. 

    The approval process for Major Change and Supplemental Type Certificate (STC) is essentially the same.

    • The CAA will issue a Major Change Approval (per Part 21 Subpart D) if the applicant is the Type Certificate Holder (TCH) for the aircraft, engine or propeller,
      and 
    • The CAA will issue an STC (per Part 21 Subpart E) for the approval of a major change from applicants other than the TCH.

    A Major Repair Approval format is common to the TCH and non-TCH alike.

    Modification of data and documentation such as the Aircraft Flight Manual and Operational Suitability Data will be processed as changes/repairs to the type design. There is no separate application.

    Eligibility

    Applicants for the CAA approval of a Major Change, Supplemental Type Certificate (STC) or Major Repair must hold an appropriate design organisation approval such as:

    • Design Organisation Approval (DOA) in accordance with Part 21 Subpart J,
      or
    • Alternative Procedures to DOA (ADOA) as per 21.A.112B(b) for some simpler STCs, 
      or
    • In the case of non-Part 21 aircraft (Annex 1) or engine/propeller, then a design organisation approval in accordance with BCAR A8-21.

    In the case of a STC on ELA1 aircraft (European Light Aircraft as defined in EU Reg 748/2012), in the absence of an organisation approval, the applicant's capability may be shown through the Certification Programme as per 21.A.112B(c).

    If DOA or ADOA is required, the scope of the certification project must be within the approved scope and Terms of Approval (TOA) of the DOA/ADOA. Applications are also accepted in cases when the certification project is simultaneously being used to demonstrate applicant competence for the issue of or extension to the scope or ToA of the DOA/DOA.

    For further information on DOAs and ADOAs see our guidance on how to apply for a Part 21 Subpart J approval.

    How to apply

    An application is made using CAA Form SRG1726NR

    Approval process

    Applicant 
    responsible
    for      		 CAA
    responsible
    for    		  Activity
    x   Submit application on CAA Form SRG1726NR and provide the initial Certification Programme
      x Check eligibility of Applicant (to ensure that the project is within the DOA scope)
    x   Provide Technical Familiarisation of the project (usually through the Certification Programme, but supplemented as necessary)
    x x Review the Certification Programme
    x x Agree the Certification Basis, Means of Compliance (MOC) and Level of Involvement (LOI)
    x   Demonstrate compliance with airworthiness and environmental requirements
      x Determine compliance as per the agreed LOI and confirm with Applicant
    x   Provide Declaration of Compliance
      x Issue Major Change/STC approval