How to Work with a Part-66 Engineer as an Owner Under Part-ML

When you manage continuing airworthiness under Part-ML and use a Part-66 engineer (or maintenance organisation) to perform and release maintenance, clear role separation is essential: you own the AMP and AD applicability; the engineer performs and releases work to your AMP and data. This article sets out how to keep AMP control, documentation, and AD tracking on the owner side, and gives nine operational principles so the partnership stays compliant and audit-ready.

1. Regulatory Context

Under Part-ML, the owner is responsible for continuing airworthiness (ML.A.201) and for the Aircraft Maintenance Programme (AMP) when it is declared by the owner (ML.A.302(e)). Part-66 (or national equivalent) certifying staff perform maintenance and release it by issuing a Certificate of Release to Service (CRS) (ML.A.801). They do not assume the owner’s responsibility for the AMP, AD applicability, or overall airworthiness.

Clear role separation is required: the owner controls the AMP and ensures compliance; the engineer performs and releases work within the scope of their authorisation and the data you provide. The legal basis is Commission Implementing Regulation (EU) No 1321/2014. See EASA Part-ML and What Does a CRS Really Mean?.

2. Practical Interpretation

AMP control: The owner owns and controls the AMP (content, revision, declaration). The engineer works to the AMP: they perform tasks as specified in the AMP and release them. They do not unilaterally change your AMP or add/remove tasks. Any change to the AMP (e.g. intervals, scope) should be agreed and documented by the owner.

Documentation responsibility: The owner is responsible for retaining the AMP, declarations, AD status, and maintenance records. The engineer (or maintenance organisation) issues the CRS and provides the supporting records for the work they did; the owner must ensure all records are complete and retained.

AD applicability ownership: Establishing which ADs apply to your aircraft (by registration, model, serial number, etc.) and when compliance is due is the owner’s responsibility. The engineer can perform the AD work and issue the CRS for that work, but the owner must ensure ADs are identified, tracked, and complied with in time.

3. Nine Operational Principles

1. You own the AMP. You declare or approve it; you decide its content and revisions. The engineer works to it, not the other way around.
2. CRS covers only the work on the form. Do not assume the engineer has verified your entire AMP or AD status. See What Does a CRS Really Mean?.
3. You own AD applicability and due dates. Provide the engineer with the list of applicable ADs and compliance status; do not rely on them to manage your AD compliance.
4. Define the work scope in writing. Before maintenance, agree what tasks will be performed (e.g. “Annual per AMP”, “AD 2024-XX”). The CRS should reflect that scope clearly.
5. Keep records in one place. You are responsible for retaining AMP, CRs, AD records, and tech log. Ensure you receive and file all CRs and CRS copies.
6. Pilot-owner tasks stay in your scope. Only you perform and sign pilot-owner tasks (if in your AMP). The engineer does not “approve” or sign them for you. See Pilot-Owner Maintenance Under ML.A.803.
7. Do not ask the engineer to sign outside their authorisation. They may only release work within their Part-66 (or equivalent) privileges and the data they use.
8. Clarify defects and rectification. If a defect is found, agree whether it is rectified now or deferred; ensure it is documented and that any deferral is permitted by the AMP/MEL.
9. Review together after major events. After an annual or major maintenance, review that all AMP tasks and ADs due at that event are completed and documented.

4. Audit Risk Scenarios

• Blurred AMP ownership. Auditors find that the engineer is effectively defining the programme or that the owner has no clear, declared AMP. Mitigation: You hold and declare the AMP; the engineer receives a copy and works to it.
• AD tracking gaps. No clear record of AD applicability or compliance; CRS mentions an AD but no supporting evidence. Mitigation: You maintain an AD applicability and compliance list; you provide it to the engineer and retain evidence of compliance.
• Incomplete CRS documentation. CRS is vague (“Inspection completed”) or does not list the tasks/ADs. Mitigation: Agree scope in advance; require CRS to state the work performed (e.g. task numbers, AD numbers).
• Missing records. Owner has no copy of the AMP, CRs, or AD status. Mitigation: You retain all records; obtain and file every CRS and supporting document.

See 12 Most Common Part-ML Audit Findings for more examples and an audit preparation checklist.

5. FAQ

Who owns the AMP – owner or engineer?

The owner owns and controls the AMP. When you declare an AMP (ML.A.302(e)), it is your programme. The engineer performs and releases work in accordance with your AMP; they do not own or approve your AMP (unless they are acting as your CAMO and then only within that contract).

Who is responsible for AD applicability?

The owner is responsible for ensuring that all applicable ADs are identified and complied with (ML.A.201). The engineer can perform the physical AD work and issue the CRS for that work, but establishing applicability (by registration, model, S/N, etc.) and tracking compliance times is the owner’s duty.

Summary: You own the AMP and AD applicability; the engineer works to your programme and releases specified work. Agree scope in writing, keep all records (AMP, CRS, AD status) in one place, and review after major events. Clear roles and complete documentation reduce audit risk and keep continuing airworthiness under control.