--- title: "ETSO-2C522 — CS-ETSO · Avioverse" description: "Helicopter Terrain Awareness and Warning System (HTAWS) Advanced Features 1 Applicability This ETSO provides the requirements that helicopter terrain…" url: "https://avioverse.aero/regulations/easa/cs-etso/subpart-b/etso-2c522" --- # ETSO-2C522 European Technical Standard Orders (CS-ETSO) · CS-ETSO · EAR revision 1 Oct 2026 IR Implementing rule ## ETSO-2C522 Helicopter Terrain Awareness and Warning System (HTAWS) Advanced Features 1 Applicability This ETSO provides the requirements that helicopter terrain awareness and warning system (HTAWS) advanced features that are designed and manufactured on or after the date of this ETSO must meet in order to be identified with the applicable ETSO marking. 2 Procedures 2.1 General The applicable procedures are detailed in CS-ETSO, Subpart A. 2.2 Specific None. 3 Technical conditions 3.1 Basic 3.1.1 Minimum Performance Standard The applicable standard is that provided in Table 1 for the intended equipment class. Table 1 — Equipment class standards | Equipment class | Equipment type | Minimum Performance Standards | | ------------------------------------- | ---------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------ | | Helicopter Offshore Operations (HOFO) | Offshore Helicopter Terrain Awareness and Warning System (HTAWS) | EUROCAE ED-285 ‘Minimum Operational Performance Standard for Offshore Helicopter Terrain Awareness and Warning System (HTAWS)’ dated March 2021. | Table 2 describes the modes covered by this ETSO standard. Table 2 — HTAWS modes | Mode | | Equipment class HOFO | | ------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------- | ------------------------------- | | 1 | Excessive rate of descent | Required | | 3A | Altitude loss during take-off | Required | | 3B | Loss of airspeed during take-off | Required | | 4A | Flight near terrain when not in landing configuration | Required | | 4B | Flight near terrain when in landing configuration | Required | | 5 | Excessive downward glideslope/glidepath deviation | ILS: Required GLS/LPV: Optional | | 7A | Airspeed versus total torque | Optional | | 7B | Vortex ring state | Optional | | N/A | Fixed altitude callout | Optional | | N/A | Terrain display | Not covered\* | | N/A | Forward looking terrain avoidance (FLTA) | Not covered\* | | N/A | Radio altitude interface | Not covered\* | | \* Local regulations on air operations may require additional modes as defined in ETSO-C194, ‘Helicopter Terrain Awareness and Warning System (HTAWS)’. | | | 3.1.2 Environmental Standard See CS-ETSO, Subpart A, paragraph 2.1. 3.1.3 Software See CS-ETSO, Subpart A, paragraph 2.2. 3.1.4 Airborne Electronic Hardware See CS-ETSO, Subpart A, paragraph 2.3. 3.2 Specific 3.2.1 Failure Condition Classification See CS-ETSO, Subpart A, paragraph 2.4. Failure of the function defined in paragraph 3.1.1 resulting in false warnings or an unannunciated loss of function is a major failure condition. A loss of the function defined in paragraph 3.1.1 is a minor failure condition. 3.2.2 Documentation The manufacturer of the offshore HTAWS shall document in its declaration of design and performance (DDP), installation and operator manuals the transition speed between the two-mode 4A alerts, and, when the corresponding modes are implemented, the intended helicopter type for which the mode 7A and/or 7B alerts have been designed. 4 Marking 4.1 General See CS-ETSO, Subpart A, paragraph 1.2. 4.2 Specific None. 5 Availability of Referenced Documents See CS-ETSO, Subpart A, paragraph 3. \[Amdt ETSO/17] IR · ETSO-2C522 — CS-ETSO · ED Decision 2022/018/R · CS-ETSO Easy Access Rules · EAR revision 1 Oct 2026 [All rules in SUBPART B – LIST OF ETSOs](https://avioverse.aero/regulations/easa/cs-etso/subpart-b) Consolidated from the EASA Easy Access Rules (revision 1 Oct 2026, 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.