---
title: "21.A.604 ETSO authorisation for an auxiliary power unit (APU) — Annex I, Initial Airworthiness · Avioverse"
description: "With regard to an ETSO authorisation for an APU: by way of derogation from points 21.A.9, 21.A.603, 21.A.610 and 21.A.621, the following points shall…"
url: "https://avioverse.aero/regulations/easa/initial-airworthiness/annex-i/section-a-technical-requirements/21-a-604"
---

# 21.A.604 ETSO authorisation for an auxiliary power unit (APU)

Annex I · Regulation (EU) No 748/2012 · EAR revision 27 Nov 2025

IR Implementing rule

## 21.A.604 ETSO authorisation for an auxiliary power unit (APU)

With regard to an [ETSO](https://avioverse.aero/glossary/easa/etso) authorisation for an APU:

(a) by way of derogation from points 21.A.9, 21.A.603, 21.A.610 and 21.A.621, the following points shall apply: points 21.A.15, 21.A.20, 21.A.21, 21.A.31, 21.A.33, 21.A.44, 21.A.47, 21.B.75 and 21.B.80. However, an ETSO authorisation shall be issued in accordance with point 21.A.606 instead of the type-certificate;

(b) by way of derogation from point 21.A.611, the requirements of Subpart D shall apply to the approval of design changes by the APU ETSO authorisation holder and design changes from other applicants classified as a minor change, and the requirements of Subpart E shall apply to the approval of design changes by other applicants classified as a major change. Where the requirements of Subpart E apply, a separate ETSO authorisation shall be issued instead of a supplemental type certificate; and

(c) the requirements of Subpart M shall apply to the approval of repair designs.

IR · 21.A.604 — Regulation (EU) No 748/2012 · Regulation (EU) 2022/201 · Initial Airworthiness Easy Access Rules · EAR revision 27 Nov 2025

[All rules in SECTION A — TECHNICAL REQUIREMENTS](https://avioverse.aero/regulations/easa/initial-airworthiness/annex-i/section-a-technical-requirements)

Consolidated from the EASA Easy Access Rules (revision 27 Nov 2025, extracted 13 Oct 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.