Aircraft retrofit: which records follow the change?

Accepting a retrofit means more than checking that the new equipment works. The records should connect the approved change, what was actually installed on this aircraft, and the information needed to operate and maintain it. This article assumes an aircraft subject to the EASA framework.

A retrofit modernises an existing aircraft, for example its avionics or cabin. A supplier announcement may justify investigating a project. It does not establish approval for the configuration of your jet or turboprop.

An STC answers a design question

A supplemental type certificate, or STC, is an approval route for a major change developed by someone other than the type-certificate holder. The EASA STC FAQ explains this framework and foreign-approval validation. Do not assume an FAA STC alone is sufficient in Europe: check the validation applicable to the case under the agreement between EASA and the FAA.

Point 21.A.115(d) in the EASA Part 21 publication limits an STC to covered configurations. The certificate alone therefore does not prove that the installation on an individual aircraft matches its approval.

The edition consulted is the November 2025 revision of the Easy Access Rules. Confirm the applicable regulatory texts and STC revisions for each project.

Make three connections visible

This is a preparation aid, not a universal regulatory checklist or a compliance statement. The exact documents depend on the change and applicable framework.

Points 21.A.6 and 21.A.7 address manuals and instructions for continued airworthiness in the same EASA publication. These instructions, often called ICA, support airworthiness after modification. Point 21.A.118A includes these obligations among those of the STC holder. Receiving later revisions matters as much as receiving the delivery-day file.

Fictional example: a cabin upgrade alongside existing equipment

A turboprop owner orders cabin equipment. The supplier presents an STC for the model. The aircraft already has an earlier electrical modification, however. The model name and STC number do not resolve compatibility between the two changes. The acceptable means of compliance AMC 21.A.115(c) explains that approval excludes pre-existing configurations not considered in the compliance demonstration.

Before acceptance, the person responsible for the records establishes the covered configuration and how that interaction is addressed. They compare installed references with the work records, then identify affected manual pages, weight-and-balance data and maintenance instructions. The expected documents are defined for this configuration, together with the points still to resolve.

The owner receives an understandable answer: what changed, on which basis, with which evidence, and who will support it. The equipment invoice remains a commercial record; it does not replace these technical connections.

Prepare the file before delivery

Name the contacts according to the question: in the maintenance organisation, the person authorised to certify the work; at the operator or its continuing-airworthiness management organisation, the person responsible for this aircraft’s technical follow-up. For unresolved design or compatibility questions, these contacts involve the STC holder or the relevant design organisation.

1. Identify the intended approval and its applicability before finalising the order.
2. Agree the project’s handover documents, including references and revisions.
3. Assign responsibility for comparing the installed configuration with the approved package.
4. Arrange integration of relevant data into aircraft support and access to updates.
5. Keep an explicit list of open points and the decisions required and the contact responsible for obtaining them.

An orderly file is not automatically complete. Its value is allowing the next operator or buyer to reconstruct the change without relying on the installation team’s memory.

Practical questions

Does an STC replace installation records?

No. Design approval and evidence of completed work answer different questions. They must be connected for the aircraft concerned.

Does every modification require an STC?

No. The approval route depends on the change and who develops it, among other factors. This article addresses a retrofit relying on an STC.

What if the supplier promises only a complete file?

Ask for project-specific deliverables, their revisions and the person responsible for each check. The phrase alone is insufficient to prepare acceptance.