6.1 Part-ML Scope, Light Aircraft Rules & Minimum Inspection Programmes

6.1 Part-ML Scope, Light Aircraft Rules & Minimum Inspection Programmes

Quick Answer: Annex Vb (Part-ML) to Regulation (EU) No 1321/2014, introduced by Commission Implementing Regulation (EU) 2019/1383 on 24 March 2020, establishes a simplified, risk-based continuing airworthiness regime specifically tailored for General Aviation (GA). Part-ML applies to other-than-complex motor-powered aircraft that are not listed in the AOC of a licensed air carrier: aeroplanes ≤ 2 730 kg MTOM, helicopters ≤ 1 200 kg MTOM certified for a maximum of up to four occupants, other ELA2 aircraft, and non-conventional aircraft within stated mass limits. Key innovations include: 1) the aircraft owner can establish and self-declare an Aircraft Maintenance Programme (AMP) without National Aviation Authority (NAA) or CAMO approval; 2) the AMP may be based on the EASA Minimum Inspection Programme (MIP) in ML.A.302(d) instead of manufacturer data, for aeroplanes, TMGs, sailplanes and balloons; 3) owner-approved deviations from Design Approval Holder (DAH) maintenance intervals and TBO escalation without authority approval; and 4) simplified defect deferral without requiring a formal Minimum Equipment List (MEL).

For nearly two decades following the adoption of Regulation (EC) No 2042/2003, European continuing airworthiness was governed by a single overarching standard: Part-M (Annex I). While Part-M effectively addressed the multi-layered complexities of high-capacity commercial jetliners, applying identical administrative burdens, CAMO oversight requirements, and authority approval processes to single-engine light aircraft and gliders imposed disproportionate financial and operational strain on the General Aviation community. To resolve this imbalance, the European Union Aviation Safety Agency (EASA) launched the General Aviation Road Map, culminating in the enactment of Part-ML (Annex Vb) under Commission Implementing Regulation (EU) 2019/1383.

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Legislative Background: The General Aviation Regulatory Revolution

Under the original Part-M regime, a private pilot operating a two-seat light aircraft was subjected to regulatory processes virtually identical to those governing a commercial airline operating a wide-body transport fleet. Developing and amending an Aircraft Maintenance Programme (AMP) required formal submission to, and technical review by, the competent National Aviation Authority (NAA), frequently taking months and incurring substantial regulatory fees. Furthermore, deviations from non-mandatory manufacturer Service Bulletins (SBs) or recommended Time Between Overhaul (TBO) calendar limits often required complex engineering justifications produced by an approved Continuing Airworthiness Management Organisation (CAMO).

Recognizing that European General Aviation suffered from regulatory over-engineering without a corresponding safety benefit, EASA established the General Aviation Safety Strategy. This strategy embraced a fundamental regulatory principle: proportionality. Safety rules must correspond directly to the complexity, kinetic energy, and operational risk of the aircraft. Part-ML was structured around four foundational pillars:

1. Elimination of Administrative Bottlenecks: Removing the legal requirement for NAA or CAMO approval of maintenance programmes for privately operated light aircraft.
2. Proportionate Maintenance Programmes: Permitting the use of a standardized EASA Minimum Inspection Programme (MIP) as an alternative to manufacturer-drafted instructions.
3. Empowerment of Certifying Personnel & Owners: Granting independent Part-66 licensed engineers the statutory privilege to maintain and release light aircraft outside approved maintenance facilities, while providing owners with legal mechanisms to escalate non-mandatory component intervals.
4. Pragmatic Defect Management: Establishing simple defect rectification and deferral pathways that do not require complex, airline-style Minimum Equipment Lists (MELs).

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Applicability and Scope of Part-ML (Rule ML.1)

Rule ML.1 defines the exact technical and operational criteria that bring an aircraft within the mandatory scope of Annex Vb. Unlike Part-M, which serves as the default continuing airworthiness code for complex and commercial aircraft, Part-ML applies strictly to light, non-commercial aviation based on explicit Maximum Take-Off Mass (MTOM) thresholds, passenger seating capacities, and operational profiles:

+-----------------------------------------------------------------------------------+
|                         PART-ML APPLICABILITY (RULE ML.1)                         |
+-----------------------------------------------------------------------------------+
| 1. Aeroplanes:            MTOM ≤ 2 730 kg                                         |
| 2. Rotorcraft:            MTOM ≤ 1 200 kg AND certified for maximum ≤ 4 occupants |
| 3. Other ELA2 aircraft (sailplanes, powered sailplanes, balloons, ELA2 airships)  |
| 4. Non-conventional aircraft: MTOM <= 1 200 kg if able to hold zero horizontal   |
|    speed in flight; otherwise MTOM <= 2 730 kg                                    |
|                                                                                   |
| CRITICAL MANDATORY OPERATIONAL EXCLUSION:                                         |
| The aircraft MUST NOT be listed in the Air Operator Certificate (AOC) of an       |
| air carrier licensed under Regulation (EC) No 1008/2008 (Commercial Air Transport)|
+-----------------------------------------------------------------------------------+

The Operational Distinction: Commercial Air Transport (CAT) vs Other Commercial Operations

A critical nuance tested extensively in EASA Part-66 Module 10 examinations is the distinction between Commercial Air Transport (CAT) and other commercial flight operations:

• Commercial Air Transport (CAT): Defined as the carriage of passengers, cargo, or mail for remuneration under an airline Air Operator Certificate (AOC). If an aeroplane weighing 2 000 kg MTOM is operated by a regional airline on an AOC for scheduled passenger flights, it cannot use Part-ML. It must comply fully with Part-M and Part-CAMO.
• Other Commercial & Training Operations: Part-ML explicitly applies to commercial operations other than CAT. This includes:
  • Commercial flight training conducted by Approved Training Organisations (ATOs) and Declared Training Organisations (DTOs);
  • Commercial Specialized Operations (commercial SPO) such as aerial photography, banner towing, agricultural cropspraying, survey operations, and parachute dropping;
  • Non-commercial operations with other-than-complex motor-powered aircraft (governed operationally by Part-NCO).

Consequently, a flight school operating Cessna 172 or Piper PA-28 aeroplanes for commercial ab-initio pilot training falls squarely under Part-ML, benefiting from its streamlined maintenance and inspection privileges.

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Comparative Analysis: Part-M vs Part-ML

Understanding the structural differences between Part-M (Annex I) and Part-ML (Annex Vb) is vital for licensed engineers navigating European continuing airworthiness:

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Aircraft Maintenance Programme under Part-ML (Rule ML.A.302)

Under European airworthiness principles, no civil aircraft may operate without an approved or accepted Aircraft Maintenance Programme (AMP). However, rule ML.A.302 fundamentally revolutionizes how an AMP is established and maintained for light aircraft.

The Owner-Declared AMP

Under ML.A.302(c), if the continuing airworthiness of a privately operated Part-ML aircraft is not contracted to an approved CAMO or Part-CAO, the aircraft owner may establish and declare an AMP under their own responsibility. The owner simply signs the declaration section of the AMP document. Crucially:

• Zero Competent Authority Approval: The declared AMP does not require submission to the National Aviation Authority (NAA) for evaluation, nor does it require any formal NAA acceptance stamp or administrative fee.
• No CAMO Endorsement: The owner does not need to hire a CAMO or CAO to approve the document.
• Contracted Scenario: If the owner elects to contract continuing airworthiness management to an approved CAMO or Part-CAO under ML.A.201, the contracted organisation develops and approves the AMP using its internal organizational procedures.

Dual Baseline Selection: DAH Data vs EASA MIP

When constructing a Part-ML AMP, rule ML.A.302(d) allows the owner or managing organisation to select between two distinct technical baselines:

1. Design Approval Holder (DAH) Maintenance Instructions: Following the Aircraft Maintenance Manual (AMM), Instructions for Continued Airworthiness (ICA), and manufacturer maintenance schedules (e.g. Cessna, Piper, Cirrus, Robinson service manuals).
2. The EASA Minimum Inspection Programme (MIP): Following the standardized inspection content set out directly in ML.A.302(d). A third option, added by Regulation (EU) 2022/1360, is the ICA issued by the declarant of a declaration of design compliance.

Alternative Intervals, Deviations, and TBO Escalation

In commercial aviation, manufacturer recommendations regarding component overhaul (Time Between Overhaul - TBO) and calendar replacement intervals are rigorously enforced by authorities. Under Part-ML (ML.A.302(c)(4)), a revolutionary flexibility is granted: the owner may decide to deviate from the DAH recommended maintenance intervals without competent authority approval.

For instance, if a piston engine manufacturer specifies a recommended TBO of 2 000 flight hours or 12 calendar years, an owner operating under Part-ML can formally record an alternative inspection interval in their declared AMP (e.g. operating the engine on-condition past 12 years based on annual compression checks, oil consumption tracking, and borescope inspections). The owner assumes legal responsibility for this deviation.

The Inviolable Boundary (Zero Deviations): While owners may deviate from non-mandatory manufacturer recommendations, rule ML.A.302(c)(4) strictly prohibits deviations from:

1. Airworthiness Directives (ADs) issued or adopted by EASA;
2. Airworthiness Limitations Sections (ALS) of the DAH instructions (e.g. mandatory life-limited structural components, wing spar fatigue life limits);
3. Certification Maintenance Requirements (CMR);
4. Specific continuing airworthiness requirements mandated by operational regulations (such as periodic 24-month pitot-static and transponder calibrations for flight in controlled airspace).

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The Minimum Inspection Programme (MIP) — ML.A.302(d)

Where the MIP actually lives. Many study notes place the MIP in Appendix I to Part-ML. That is wrong: Appendix I to Part-ML is the continuing airworthiness management contract, Appendix II is Limited Pilot-owner maintenance, Appendix III is Complex maintenance tasks not to be released by the Pilot-owner, and Appendix IV is the Airworthiness Review Certificate (EASA Form 15c). The MIP content and intervals are in the rule text at ML.A.302(d).

ML.A.302(d) establishes the technical content of the EASA Minimum Inspection Programme (MIP). The MIP was engineered to provide a robust, safety-focused inspection checklist that eliminates non-safety-critical manufacturer servicing overhead while ensuring thorough examination of primary structural and mechanical systems.

Standard MIP Inspection Intervals (ML.A.302(d)(1))

• Aeroplanes, Touring Motor Gliders (TMGs) and balloons: every annual or 100-hour interval, whichever comes first, to which a tolerance of 1 month or 10 hours may be applied. The next interval is calculated from the time the inspection takes place.
• Sailplanes and powered sailplanes other than TMGs: every annual interval, to which a tolerance of 1 month may be applied. The next interval is calculated from the time the inspection takes place.
• Rotorcraft: there is no MIP. ML.A.302(d) closes with an explicit statement that, as long as Part-ML does not specify an MIP for aircraft other than aeroplanes, sailplanes and balloons, their AMP shall be based on the ICA issued by the DAH. A Part-ML helicopter therefore cannot use the MIP route at all — this is a favourite examination trap.

Core Technical Content of the MIP (ML.A.302(d)(2))

The MIP is not a 20-item checklist. ML.A.302(d)(2) lists the following, as applicable to the aircraft type:

(a) Servicing tasks as required by the DAH’s requirements.

(b) Inspection of markings.

(c) Review of weighing records and weighing in accordance with Regulation (EU) No 965/2012, Regulation (EU) 2018/395 and Regulation (EU) 2018/1976.

(d) Operational test of the transponder (if installed).

(e) Functional test of the pitot-static system.

(f) For aeroplanes, as applicable to the power plant: operational tests for power and rpm, magnetos, fuel and oil pressure and engine temperatures; for engines with automated engine control, the published run-up procedure; for dry-sump engines, turbocharged engines and liquid-cooled engines, an operational test for signs of disturbed fluid circulation; and, for a power plant other than a piston engine, the maintenance tasks defined in the DAH’s ICA.

(g) Inspection of the condition and attachment of structural items, systems and components corresponding to the following areas:

• Aeroplanes: airframe; cabin and cockpit; landing gear; wing and centre section; flight controls; empennage; avionics and electrics; power plant; clutches and gearboxes; propeller; and miscellaneous systems such as the ballistic rescue system.
• Sailplanes and powered sailplanes: airframe; cabin and cockpit; landing gear; wing and centre section; empennage; avionics and electrics; power plant (for powered sailplanes); and miscellaneous systems such as removable ballast, drag chute and controls, and the water ballast system.
• Hot-air balloons: envelope; burner; basket; fuel containers; equipment and instruments.
• Gas balloons: envelope; basket; equipment and instruments.

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Defect Management and Deferral (Rule ML.A.403)

Under Part-M, operating an aircraft with an inoperative instrument or defective system typically requires consulting a complex, approved Minimum Equipment List (MEL). In contrast, rule ML.A.403 introduces a pragmatic defect management pathway designed for general aviation:

1. Mandatory Safety Evaluation: Any defect that hazards the safety of flight must be rectified before the next flight. The aircraft cannot legally fly with an unairworthy condition.
2. Defect Deferral Authority: If a defect does not compromise flight safety, it may be formally deferred by:
   • An appropriately licensed certifying staff member (independent Part-66 or Part-CAO / Part-145 personnel); or
   • The pilot-owner, provided the defect relates to a task within the scope of pilot-owner maintenance defined in Appendix II.
3. Elimination of Complex MEL for Non-Commercial Flights: For private operations governed by Part-NCO (Non-Commercial Operations with Other-than-Complex Motor-Powered Aircraft), an approved MEL is not required. Instead, deferral is guided by NCO.GEN.155, which permits flight with inoperative instruments or equipment provided the item is:
   • Not required by the airworthiness certification basis (e.g. Type Certificate Data Sheet - TCDS or Aircraft Flight Manual - AFM Kind of Operations Equipment List - KOEL);
   • Not required by airspace or operational rules (e.g. VFR day, VFR night, or IFR navigation mandates);
   • Not mandated by an applicable Airworthiness Directive (AD).

When a defect is deferred under ML.A.403, the certifying staff or pilot-owner must record the deferral in the aircraft technical log or logbook, placard the inoperative component clearly as "INOPERATIVE", and isolate or deactivate the system (such as pulling and collaring its associated circuit breaker).

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Practical Maintenance Scenario: AMP Declaration & TBO Escalation

Operational Context

A private owner operates a Piper PA-28-181 Archer III (MTOM 1 157 kg) for recreational flying and personal travel under Part-NCO. The aircraft is equipped with a Lycoming O-360-A4M engine. The engine reaches 2 000 flight hours, which corresponds to the manufacturer's recommended Time Between Overhaul (TBO) specified in Lycoming Service Instruction 1009.

Regulatory Assessment under Part-ML:

1. Applicability: The aeroplane has an MTOM of 1 157 kg (well below the 2 730 kg threshold) and is not on an air carrier AOC. Therefore, Part-ML applies.
2. AMP Declaration: Under ML.A.302, the owner establishes a declared AMP based on the EASA Minimum Inspection Programme (MIP) set out in ML.A.302(d). No National Aviation Authority approval is requested or required.
3. TBO Escalation: Under ML.A.302(c)(4), the owner elects to deviate from Lycoming's recommended 2 000-hour TBO. The owner incorporates an 'on-condition' maintenance escalation procedure into the declared AMP, requiring differential cylinder compression checks, engine oil spectrographic analysis every 50 hours, oil filter pleat cutting, and exhaust valve borescope inspection at each annual MIP inspection.
4. Legal Status: The engine can legally continue operating past 2 000 hours under European law under the owner's legal responsibility, without any waiver or approval from EASA or the NAA.

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EASA Module 10 Examination Tips & Regulatory Traps

• Mass & Occupant Thresholds: Memorize the precise limits in ML.1(a): Aeroplanes ≤ 2 730 kg MTOM; helicopters ≤ 1 200 kg MTOM certified for a maximum of up to four occupants; other ELA2 aircraft; and non-conventional aircraft (≤ 1 200 kg if able to hold zero horizontal speed in flight, otherwise ≤ 2 730 kg). The third category is other ELA2 aircraft — not sailplanes and balloons with no mass ceiling. Gas airships other than ELA2 are Group 1 aircraft and fall outside Part-ML.
• The AOC Disqualification: Remember that if a light aircraft is listed on an AOC for Commercial Air Transport, Part-ML is completely inapplicable—it must follow Part-M.
• Commercial Flying Schools (ATO/DTO): Flight school training aircraft fall under Part-ML because flight instruction is not commercial air transport under an AOC.
• AMP Approval Trap: An owner-declared AMP under ML.A.302 requires zero authority approval. If an exam question asks: "Who approves the declared AMP of a private Cessna 172 under Part-ML?" The correct answer is: The owner declares it; no authority approval is required.
• Inviolable Items: The owner can escalate manufacturer recommended TBO and service intervals, but can never deviate from Airworthiness Directives (ADs) or Airworthiness Limitations (ALS).
• MIP Interval: For aeroplanes, TMGs and balloons the MIP interval is annual or 100 hours, whichever comes first (tolerance 1 month or 10 hours). For sailplanes and powered sailplanes other than TMGs it is annual (tolerance 1 month). Rotorcraft have no MIP — their Part-ML AMP must be based on the DAH’s ICA.
• MIP Location Trap: The MIP is in ML.A.302(d), not in Appendix I. Appendix I to Part-ML is the continuing airworthiness management contract; Appendix II is limited Pilot-owner maintenance; Appendix III lists the complex maintenance tasks the Pilot-owner may not release; Appendix IV is the ARC (EASA Form 15c).