GM1 SPA.HOFO.160(c)(2) Helicopter terrain awareness and warning system (HTAWS)

CAA ORS9 Decision No. 26

(a) The alert envelopes defined in EUROCAE ED-285/RTCA DO-376 may be used in lieu of those defined in CAP 1519 for upgrades to HTAWS installations and new HTAWS installations performed prior to 1 January 2025.

(b) Where available for the helicopter type, the Mode 7/7a alert envelopes defined in UK CAA CAP 1519 may be used. Alternatively, or where no Mode 7/7a alert envelope is defined in UK CAA CAP 1519, Mode 7 alert envelopes may be derived using a representative sample of flight data collected from normal revenue service operations using the methodology described in UK CAP 1538. Mode 7/7a envelopes may also be developed using the methodology described in Appendix B of EUROCAE ED-285/RTCA DO-376; either fixed or variable Mode 7a envelopes may be implemented.

(c) Additional alerting functions may be included, provided that an acceptably low nuisance alert rate can be demonstrated.

(d) Where Forward-Looking Terrain Avoidance (FLTA) functionality is provided, operational experience indicates that it will likely be necessary to remove offshore oil & gas installations from the obstacle database in order to prevent an excessive nuisance alert rate.

(e) Inadvertent use of any non-offshore mode while operating offshore may result in reduced protection and/or and excessive nuisance alerts. Inadvertent use of the offshore mode while operating onshore may result in nuisance alerts, for example, when flying ILS approaches at high ground speeds.