HTAWS: Terrain Awareness and Warning
FLTA and GPWS, and every alert and what triggers it — the onshore-only baseline version of this system.
Source: AW169 RFM Supplement 13 (Helicopter Terrain Awareness and Warning System). This AW169 Standard configuration has no OFFSHORE operating modes and no SAR mode — see the separate AW169 EP note for that configuration.
What it does
HTAWS, embedded in the Collins MFD-2810, gives terrain and obstacle awareness through two independent functions: Forward Looking Terrain (and Obstacle) Alerting (FLTA), which looks ahead of the aircraft's flight path, and Ground Proximity Warning System (GPWS), which reacts to the aircraft's actual proximity to terrain. Terrain/obstacle display is selectable on PFD and MFD; an obstacle is defined as any human-made structure higher than 50 ft AGL.
This configuration provides four operating modes: Mode 1 (excessive rate of descent), Mode 3 (descent after take-off or missed approach), Mode 4 (flight into terrain when not in landing configuration), Mode 5 (excessive downward deviation from an ILS glideslope). There is no OFFSHORE option and no SAR mode on this configuration.
Alerts
| Priority | Aural | Red caption | Amber caption |
|---|---|---|---|
| 1 | PULL UP | PULL UP | — |
| 2 | WARNING TERRAIN | TERRAIN | — |
| 2 | WARNING OBSTACLE | OBSTACLE | — |
| 3 | CAUTION TERRAIN | — | TERRAIN |
| 3 | CAUTION OBSTACLE | — | OBSTACLE |
| 4 | THREE HUNDRED / active height callouts | — | — |
| 5 | TOO LOW GEAR | — | TOO LOW GEAR |
| 6 | SINKRATE | — | SINKRATE |
| 7 | DON'T SINK | — | DON'T SINK |
| 8 | GLIDESLOPE | — | GLIDESLOPE |
Reduced-sensitivity modes
LOW ALT, TACT ALT and OFF AIRPORT reduce the alert envelope for low-altitude or non-airport operations. None of them may be selected under IMC, except where a specific approved procedure allows it — the RFM names the FMS Oil Rig Approach as an example.
Database limitation
The terrain/obstacle database must be the latest update for the region being flown, and it only covers a defined latitude interval, per the HTAWS Pilot's Guide.
Inhibiting and status messages
TAWS INHIBIT disables all alerts except altitude callouts (the terrain map image stays up). AUDIO INHIB mutes cautions only — not callouts, not warnings — and clears itself after 5 minutes if not deselected first. OFF APT reduces nuisance alerts when landing somewhere not in the database, without disabling the system. G/S CANCEL suppresses the glideslope-deviation alert when the ILS isn't in the database.
Failure captions: TAWS FAIL (no valid HTAWS info — both FLTA and GPWS gone), TERRAIN (terrain data unavailable), GPWS INOP, FLTA INOP, OBST INOP (obstacle database missing, or too many obstacles in view — the system only ever displays the 100 nearest above the altitude clearance level).