IRImplementing 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