Section 8 Terrain Awareness Warning System
1
st
Ed Nov 2018
IDU-450 EFIS Software Version 8.0H (Rotorcraft)
8-11
Figure 8-9: Rotorcraft GPWS Mode 3
8.7.
Flight into Terrain when not in Landing Configuration (GPWS
Mode 4)
GPWS Mode 4 function is present in Enhanced HTAWS and uses aircraft
speed information and AGL altitude to alert when descending into terrain
without properly configuring the aircraft for landing. There are two Mode 4
envelopes: Mode 4A, which gives cautions when landing gear is in other
than landing configuration, and Mode 4B, which gives cautions when
landing gear are in other than landing configuration. Applicability of Mode
4 envelopes to aircraft types are as follows.
Table 8-7: HTAWS GPWS Mode 4 Envelopes
Landing Gear
Mode 4A
Mode 4B
Retractable
Landing Gear Up
Not Applicable
Fixed
Not Applicable
Not Applicable
Mode 4 envelope consists of low-speed and high-speed regions.
Table 8-8: HTAWS GPWS Mode 4 Alerting Criteria
Region
Caution Flag
Single Voice Alert
Low-Speed
“Too Low Gear”
High-Speed
“Too Low Terrain”
Autorotation expansion, when
engaged, regardless of speed
“Too Low Gear”
Mode 4 alerting criteria require the Mode 4 envelope to be entered from
above so changing aircraft configuration while within a Mode 4 envelope
does not generate an alert.
0
100
200
300
400
500
600
0
1000
2000
3000
4000
Height Above
Terrain
(FT)
Barometric Altitude Sink Rate (fpm)
Rotorcraft Mode 3