TAWS Regulations¶
Class A¶
Class A TAWS is mandatory for all turbine-powered civil airplanes configured with 10 or more passenger seats (excluding any pilot seats). A Class A system provides comprehensive, high-integrity protection against Controlled Flight Into Terrain (CFIT) through an integrated suite of alerting modes and continuous situational awareness displays.
Required Alerting Modes¶
Mode 1: Excessive descent rate (Sink Rate, Pull Up)
Mode 2: Excessive terrain closure rate (Terrain Terrain, Pull Up)
Mode 3: Altitude loss after takeoff or go-around (Don't Sink)
Mode 4: Unsafe proximity to terrain (Too Low - Terrain / Gear / Flaps)
Mode 5: Excessive downward deviation from an ILS glideslope
Mode 6: Minimums callouts and advisory voice outputs
Mode 7: Predictive windshear detection and reactive warnings (not modelled in the Twotter)
Forward-Looking Terrain Avoidance (FLTA): Must calculate a projected flight path to provide early clearance cautions and impending hazard warnings.
Terrain Clearance Floor (TCF): Must establish an increasing terrain-protection floor independent of local barometric altimetry settings near runways.
Display Requirements¶
Must include a dedicated, continuous visual terrain situational awareness display (typically integrated into an MFD, PFD, or dedicated screen) providing clear, color-coded threat differentiation (Green for clear, Yellow for caution, Red for warning).
Class B¶
Class B TAWS is mandatory for turbine-powered civil airplanes configured with 6 to 9 passenger seats (excluding any pilot seats). (Note: Operators of aircraft exempt from Class A/B mandates frequently elect to install Class B equipment as a voluntary safety enhancement).
Class B systems provide scaled-down yet robust terrain protection tailored for smaller turbine aircraft operations, balancing high-level safety alerting with spatial and economic constraints common in light corporate and regional fleets.
Required Alerting Modes¶
Includes core reactive modes adapted for smaller performance profiles (specifically Modes 1, 3, 4, and 6).
Forward-Looking Terrain Avoidance (FLTA): Must provide predictive terrain clearance cautions and warnings.
Terrain Clearance Floor (TCF): Must feature the runway-centric terrain protection floor.
Display Requirements¶
While a graphical terrain display is strongly recommended and standard on modern Class B installations, legacy configurations may satisfy minimum requirements via visual caution/warning lamps and audio-only voice annunciations, provided a regional terrain database is actively monitored by the system.
Reviewed 2026-08-11.