ETSO, FAA TSO and Installation Approval: What Each Covers

What does an ETSO authorisation approve?

An ETSO authorisation approves an article against the applicable European Technical Standard Order, including any approved deviations. It supports the assessment of equipment for an aircraft, but it does not approve that installation. The aircraft installation and the release of the individual item remain separate checks. EASA’s ETSO explanation makes that boundary explicit.

The distinction between a standard and an authorisation also matters. A supplier naming an ETSO or TSO has identified a standard. The next question is which approved article and configuration it is offering. The FAA’s TSO overview explains the US design, production and installation boundaries.

Where certification specifications fit

For a type certificate, EASA establishes and notifies the applicant of the type-certification basis under 21.B.80. Its starting point is the airworthiness certification specifications applicable on the application date, together with relevant special conditions.

That is a starting point with qualifications. The rule allows later specifications when chosen or required, accepted alternatives with compensating safety factors, and other means accepted or prescribed by EASA in the cases it describes. A project’s basis therefore needs to be read as a defined set of requirements. Substituting today’s latest CS amendment can give the wrong answer about what that project demonstrated.

The type-certification guide explains the certificate, its data sheet and changes. The airworthiness lifecycle guide places those approvals alongside production and in-service responsibilities.

ETSO is one approval route

21.A.303 distinguishes compliance through product certification, the ETSO route where applicable, and officially recognised standards for standard parts. An ETSO article does not become a “standard part” merely because it meets a technical standard. Where approval is explicitly required, 21.A.305 requires compliance with the applicable ETSO or specifications EASA recognises as equivalent in the particular case.

The authorisation brings a defined manufacturing privilege:

For engineering or purchasing, the marking is a useful starting point. The supporting documents explain what the approval covers.

Read the Declaration of Design and Performance

The Declaration of Design and Performance (DDP) connects the article’s identity to its standard and demonstrated performance. 21.A.608 calls for article/design/test identification, rated performance where appropriate, a compliance statement, test-report and manual references, compliance levels and accepted deviations. It also requires the holder’s or authorised representative’s date and signature.

The acceptable means of compliance, AMC 21.A.608, provides a standard form. It includes modification standard, environmental qualification and limitations affecting aircraft application. Examples include temperature and altitude categories, vibration, power input and mounting restrictions, depending on the article.

A useful document review asks whether the declared qualification and limits match the proposed installation. A familiar model name alone cannot answer that question. Keep the DDP issue and modification standard with the engineering assessment so another person can see which configuration was considered.

What an approved deviation means

A deviation has its own approval requirements:

Point (b) requires the request and supporting data to be submitted to EASA. Read an accepted deviation alongside the DDP: it tells you where the article’s approved basis differs from the published standard. It gives an installer no authority to approve a further departure.

How FAA TSO and ETSO acceptance works

The EU–US Technical Implementation Procedures (TIP), section 3.3.3.1, provide for acceptance of the exporting authority’s TSO or ETSO authorisation without a duplicate approval from the importing authority. Conditions include evidence of conformity and, where relevant, substantiated deviations or exemptions approved by the exporting authority. Installation approval remains separate. Read TIP Revision 7 & 7.1.

This acceptance operates within the agreement’s scope. EASA’s EU–US bilateral page expressly notes that the agreement does not apply to Norway, Iceland, Switzerland or Liechtenstein solely through their EASA membership. The applicable arrangement needs checking for the transaction concerned.

Also check the functions being claimed. TIP section 3.3.3.3 addresses data for additional non-TSO functions integrated into approved equipment. Its conditional acceptance of that data does not turn those functions into an installation approval.

Five checks before ordering or planning installation

Use these as engineering questions to organise the evidence:

1. What aircraft and installation are proposed? Identify the aircraft configuration and the applicable design approval route and data. Establish the installation requirements before comparing equipment.
2. What exact article is offered? Match the manufacturer, model or part number and modification standard to the authorisation and DDP. Resolve a mismatch before treating documents as evidence for that item.
3. What performance and limits are declared? Read the ETSO/TSO revision, compliance levels, environmental qualification, accepted deviations and relevant installation restrictions. EASA’s ETSO listing helps locate the particular standard.
4. Which acceptance route applies? For equipment crossing regulatory systems, establish the applicable bilateral scope and conditions. Similar approval names do not settle territorial or product coverage.
5. What supports the individual item and its installation? Check its release records, condition and applicable maintenance data. 145.A.42 and its guidance connect installation to the specified component, including part number, modification status and limitations.

For the last check, continue with parts, appliances and release documents. That guide explains why an acceptable release document and an eligible aircraft installation are different decisions.

Sources and revision scope

The Part-21 text used here comes from the EASA Initial Airworthiness Easy Access Rules, 27 November 2025 revision; the component-installation text comes from Continuing Airworthiness, 2 September 2025 revision. The FAA definition was checked in the 14 CFR Part 21 corpus dated 6 October 2026, at 21.601(b). The bilateral reference is TIP Revision 7 & 7.1.

These consolidation dates identify the source editions, rather than a legal amendment cut-off. Later amendment scope was checked for the provisions discussed here. Consult EASA’s initial-airworthiness regulatory index for subsequent changes and the individual ETSO for its applicable technical revision. This guide explains the approval structure; it does not determine eligibility for a particular aircraft.