• Introduction

    Part-ML and Part-CAO provide a proportionate framework for continuing airworthiness to correspond to the lower risks associated with 'Light Aircraft' in general aviation.

    Part-ML is a continuing airworthiness standard that sets out the maintenance that must be performed in order to ensure that the aircraft is airworthy. It also establishes the responsibilities of persons or organisations involved in the activities related to the airworthiness of the aircraft.

    Part-CAO provides a new set of requirements for a Combined Airworthiness Organisation. This organisation may perform CAMO activities or Maintenance Organisation activities, or both, but limited to non-complex aircraft not used by a licenced air carrier.
    Part-ML became applicable on 24 March 2020, Part-CAO will be fully implemented by 24 September 2021.


    Part-ML simplifies existing maintenance rules and offers a less prescriptive and burdensome approach to maintenance programmes, airworthiness reviews, defects deferments and TBO extensions. It also provides more privileges for pilots, owners, independent certifying staff and small maintenance organisations. For example:

    • The CAA will no longer be involved in the approval of maintenance programmes for Light aircraft. 
    • A new Airworthiness Review Certificate (EASA Form 15c) has been introduced that can be issued by the CAA, by an approved organisation or by independent Part-66 engineers with an appropriate authorisation.
    • CAA Generic Requirements (e.g. GR No.24) have been revised to remove their applicability to EASA Aircraft Types, including those within the scope of Part-ML


    Part-CAO introduces a new combined Maintenance and Airworthiness Management Organisation for 'Light Aircraft' and aircraft up to 5700 kg MTOW within the revised scope of Part-M:

    • Existing Part M Subpart F and Subpart G approvals will gradually be replaced with a new Combined Airworthiness Organisation approval, Part-CAO (pronounced “cow”)
    • The transition period will end on 24 September 2021. After this date Part M Subpart F and Subpart G approvals will no longer be valid.
    • Applications for a Part-CAO approval can be made using this online application form. Applications should include a Combined Airworthiness Exposition (CAE) and an internal audit to show that your organisation is in compliance with the requirements. The CAE document should be in the format specified in AMC1 CAO.A.025 Combined airworthiness exposition (CAE) . The Part-CAO Example Expositions below are in the correct format.
    • For Part-CAO transition, Organisations that hold either a Part-MF or Part-145 approval should reference these Approval Numbers (as applicable) in the transition application.
    • There is currently no fee for a transition from a stand-alone Part-MG approved organisation to a Part-CAO approved organisation. A stand-alone Part-MG is an organisation that does not hold a Part-MF approval and wishes to retain their existing Part-145 approval.

    Independent Certifying Staff

    Part-ML introduces an independent certifying staff authorisation which allows licenced engineers to carry out the airworthiness review and issue the Airworthiness Review Certificate in conjunction with the annual inspection for light aircraft within the scope of Part-ML:

    • The authorisation is issued after the applicant has carried out an Airworthiness Review under supervision by the competent authority (CAA).
    • The authorisation is limited by Part-ML and the scope of aircraft on the applicant’s licence.
    • Existing ELA 1 authorisations are not valid after 24th March 2020 due to the change in regulations
    • Applications for an independent certifying staff authorisation should made using Form SRG1015 be submitted to apply@caa.co.uk with 'ML.A.901 Authorisation' in the subject line.

    Additional information (General)

  • CAA LAMP has been withdrawn. All aircraft within the scope of Part-ML must transfer to a Part-ML-compliant maintenance programme at the next Airworthiness Review. CAA LAMP cannot be used after 24 March 2021. 

    Part-ML will become applicable on 24 March 2020. To align UK requirements with this EASA rule change, GR No.17 and GR No.24 will be revised to remove their applicability to aircraft maintained under Part-ML.

    After this date, deviations from the Design Approval Holder's Instructions for Continuing Airworthiness (DAH ICA), such as the extension of time between overhaul (TBO) intervals, should be evaluated using a risk-based approach.

    The risk-based approach should consider aspects such as the operation of aircraft, type of aircraft, hours/years in service, maintenance of the aircraft, compensating measures, redundancy of components, etc.

    Alternative tasks or intervals (e.g. escalations) to the DAH ICA by the CAMO or CAO do not need to be approved by the competent authority. Justification of these deviations are to be documented and retained by the CAMO or CAO.

    Where an aircraft subject to Part-ML is not used for commercial operations and the owner elects to manage the continuing airworthiness of the aircraft themselves, the owner issues a declaration for the maintenance programme and in this case, no justification of such deviations is required.

    Details can be found in Part-ML Paragraph ML.A.302 and AMC1 ML.A.302(c)(3). Owners, operators and approved organisations should ensure they are familiar with the revised regulations as well as the safety implications of any proposed deviations from the DAH ICA.

    It is important to note that deviations with respect to tasks classified as mandatory (e.g. Airworthiness Directives, requirements specified on the type certificate data sheet, airworthiness limitations) are not permitted.

  • Additional information (Maintenance and Continuing Airworthiness Organisations)

    The following information is intended to provide simple guide to some of the changes in regulations when Part-ML became applicable for Part-CAO, Part-145 and Part M Subpart F organisations maintaining aircraft in accordance with the revised Part-M and Part-ML.

    In all cases the EASA regulations and AMC/GM are the definitive documents. 

  • It is not possible to increase the scope of approval during the transition process.

    If an organisation wishes to expand its scope of approval it must transition and subsequently apply for a variation.   

    For example, if you only have a Part M, Subpart G approval you cannot add aircraft maintenance privileges (the old Part M, Subpart F) during the transition process.  

    A Part-CAO organisation can maintain and manage aircraft within the scope of Part-ML.

    A Part-CAO organisation can also maintain and manage aircraft within the scope of Part-M that are not classified as complex motor-powered aircraft and are not listed in the air operator certificate of an air carrier licensed in accordance with Regulation (EC) No 1008/2008. 

    A full list of aircraft and operations that can only be managed and maintained by Part-CAMO/Part-145 Organisations is in Part M, M.A.201 (e), (f) and (g). Aircraft in this category are not within the scope of a Part-CAO.

    These documents have been produced by the UK CAA as examples of a compliant Part-CAO Combined Airworthiness Exposition (CAE) and the associated BCAR A8-24 & A8-25 supplements.

    They have been produced with the intent of assisting new applicants and those organisations transitioning from Part-MF & Part-MG. The notes page at the beginning of each document contains important information to be read prior to use of the content:

    If an organisation has aircraft in the scope of Part-M and Part-ML it must have Airworthiness Review staff qualified in accordance with both Part M, M.A.707 and part-ML, ML.A.904.

    If you maintain both classes of aircraft, you need procedures appropriate to each set of regulations. Part ML does not allow the voluntary application of Part M requirements to aircraft in the scope of Part ML.  

    Parts released by a Part-CAO under a Component rating can be used by a Part-145 organisation, but the components cannot used for aircraft included in Part M, M.A.201 (e), (f) and (g). 

    This means if an aircraft can only be managed by a Part-CAMO organisation, parts released by a Part-CAO cannot be used.

    As it says on the Form 1 “This certificate does not automatically constitute authority to install the item(s).”  

    Since 24 March 2020, it is only possible to issue an EASA Form 15c for aircraft within the scope of Part-ML (New Issue).

    If an aircraft holds a current EASA Form 15b, that has not been extended for either the first or second time, it is possible to extend this ARC until the first and second extensions expire. This is only possible where the aircraft has been continuously managed for the previous 12 months by the CAMO or CAO granting the extension after ensuring that the other requirements of ML.A.901(c) are also met. 

    Approved organisations may issue Airworthiness Review Certificates (ARCs) directly using the Word version of Form 15C, suitably amended with their approval number, aircraft details and dating protocols: Download Form 15C Issue 3 (Word Document).

    A copy of the ARC issued or extended for an aircraft must be sent to the CAA apply@caa.co.uk  within 10 days, as required by ML.A.903 (h).


  • 'Light aircraft'

    'Light aircraft' means the following non-complex motor-powered aircraft not listed in the air operator certificate of an air carrier licensed in accordance with Regulation (EC) No 1008/2008:

    1. aeroplanes of 2,730 kg maximum take-off mass (MTOM) or less;
    2. rotorcraft of 1,200 kg MTOM or less, certified for a maximum of up to 4 occupants;
    3. other ELA2 aircraft (e.g. sailplanes, balloons, small airships).


    More information will be published as soon as it is available. Please subscribe to our SkyWise alerting system so we can let you know when new information has been added.