Part-M vs Part-ML is not a question about aircraft size, though mass is part of it. It is a question about which of two entirely separate continuing airworthiness regimes an aircraft sits in — and the same airframe can move between them without a single bolt changing.

The boundary is drawn in ML.1

Point ML.1 of Annex Vb to Regulation (EU) No 1321/2014 sets the scope:

In accordance with paragraph 2 of Article 3, this Annex (Part-ML) applies to the following other than 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.

Three conditions, all of which have to hold. The aircraft must not be complex motor-powered. It must not be listed on the AOC of a licensed air carrier. And it must fall within one of the three categories.

Miss any one and the aircraft is a Part-M aircraft. The AOC condition is the one that catches people out, because it has nothing to do with the aircraft at all. A 2 000 kg aeroplane sitting comfortably inside the mass threshold becomes a Part-M aircraft the moment it is added to a licensed carrier’s certificate.

What actually changes when you cross the line

The scope test is the easy part. What matters operationally is that Part-ML is not a lighter-touch version of Part-M with the same architecture. Several mechanisms exist in one and simply have no counterpart in the other. That is by design: Part-ML arrived with Commission Implementing Regulation (EU) 2019/1383, which inserted Annex Vb alongside Part-CAMO and Part-CAO rather than trimming the existing annex.

The maintenance programme: declared, or approved

This is the largest single difference. Under Part-M, point M.A.302(b) is unambiguous:

The AMP and any subsequent amendments thereto shall be approved by the competent authority.

An indirect approval procedure through a CAMO or CAO is available under M.A.302(c), but the destination is still approval. Under Part-ML, point ML.A.302(b) offers a genuinely different route:

The AMP and any subsequent amendments thereto shall be, alternatively:
(1) declared by the owner in accordance with point (c)(7) of point ML.A.302, where the continuing airworthiness of the aircraft is not managed by a CAMO or CAO;
(2) approved by the CAMO or CAO responsible for managing the continuing airworthiness of the aircraft.

An owner can declare their own maintenance programme. No authority approval, no organisation in the loop. What the declaration costs them is set out in ML.A.302(c)(7), which requires the AMP to contain a signed statement by which the owner declares

that this is the AMP for the particular aircraft registration and that he is fully responsible for its content and, in particular, for any deviations from the DAH’s recommendations

Responsibility moves rather than disappearing. That is the actual trade in Part-ML: less process, more personal accountability.

Who may issue the airworthiness review certificate

Both regimes require a periodic airworthiness review and both issue an ARC valid for one year. Who may issue it is where they part company.

Point ML.A.901(b) gives four routes: the competent authority; an appropriately approved CAMO or CAO; the approved maintenance organisation while performing the 100-hour or annual inspection contained in the AMP; and, for aircraft operated under Part-NCO and the equivalent balloon and sailplane cases, independent certifying staff while performing that same inspection.

The third and fourth routes have no Part-M equivalent. A maintenance organisation cannot issue an ARC under Part-M, and independent certifying staff do not feature at all. Under Part-M the review runs through the competent authority or a suitably privileged CAMO or CAO, with M.A.901 building its whole structure around the concept of a controlled environment — an aircraft continuously managed by a unique CAMO or CAO and maintained by approved organisations for the preceding 12 months.

One sharp edge worth knowing: ML.A.901(b) states that ARCs issued by independent certifying staff holding a national qualification, rather than a Part-66 licence, do not benefit from mutual recognition when the aircraft transfers to another Member State.

Pilot-owner maintenance

Point ML.A.803 lets a qualifying pilot-owner issue a certificate of release to service after limited maintenance set out in Appendix II to Part-ML. To qualify, the person must hold a valid pilot licence or equivalent for the aircraft type or class rating, and own the aircraft as sole or joint owner.

It is narrower than it first sounds. The AMP has to identify whether pilot-owners are authorised to perform maintenance at all, under ML.A.302(c)(6), and the authorisation reaches only the tasks in Appendix II. But the principle — that the person flying the aircraft can lawfully sign for work on it — is foreign to Part-M.

Extending the ARC

Both allow two consecutive one-year extensions, but on different tests. Under ML.A.901(c) an appropriately approved CAMO or CAO may extend where the aircraft has been continuously managed by that organisation for the previous 12 months, maintained by approved organisations over the same period, and where the organisation has no evidence or reason to believe the aircraft is not airworthy. Notably, the extension is available regardless of which of the four routes originally issued the ARC.

Part-M ties its extension to the controlled-environment concept and, under M.A.901(c), to aircraft above 2 730 kg MTOM in that environment or used by licensed air carriers — and the organisation may only extend an ARC it has issued.

The comparison in one table

Why this matters more than it looks

Because the boundary is not fixed. Mass and complexity are properties of the aircraft, but the AOC condition is a property of how the aircraft is being used, and that changes with commercial decisions rather than engineering ones.

An operator adding a light aircraft to its AOC has not modified anything. It has moved that aircraft from a regime where the owner could declare the maintenance programme into one where the competent authority must approve it; from four possible ARC routes to two; and out of pilot-owner maintenance entirely. If nobody notices the transition, the first indication is usually a finding.

The same applies in reverse when an aircraft comes off an AOC, and to any aircraft sitting close to 2 730 kg where a mass change could cross the threshold.

Test yourself on where the line falls with the free Part-M & Part-CAMO quiz: 300 timed questions on EASA continuing airworthiness, in three levels.

Training on this

If you want the framework explained from the ground up, our free Part-M and Part-CAMO: An Introduction covers where the rules come from and what a CAMO does, in about 30 minutes at no cost.

This is the scope waypoint from that course, free to watch here. It works the same boundary from the other direction: instead of starting at ML.1 and reading outwards, it starts from the two tests that settle most cases in practice — whether the aircraft is complex motor-powered, and how it is being used.

For the regulation covered end to end, including how Part-M relates to the other annexes, see the Part-M and Part-CAMO Familiarisation course. Staff who already work in continuing airworthiness and need to go deeper into how each process is built should look at the Part-M and Part-CAMO Specialisation course.

Further reading

• Part-CAMO: A Complete Compliance Guide — the organisation side of continuing airworthiness
• Airworthiness Directive Management — one obligation that applies whichever regime you are in
• How to Write a CAME — for organisations that manage continuing airworthiness under either annex

Frequently asked questions