Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 14
RADIO ALTITUDE (FEET)
0
500
1000
1500
2000
2500
0 200 400 600
ALTITUDE LOSS (FEET)
"DON'T SINK"
"DON'T SINK"
FIGURE 1.3.1.3-2: MODE 3 - ALTITUDE LOSS AFTER TAKEOFF (TURBOFAN)
The altitude loss variable is based on the change of altitude (MSL) from the beginning of the inadvertent descent. The
amount of altitude loss, which is permitted before an alert is given, is a function of the height of the aircraft above the terrain,
as shown in Figures 1.3.1.3-1 and 1.3.1.3-2. Mode 3 is enabled after takeoff or go around, when landing gear or flaps are not
in landing configuration. It stays enabled until the EGPWC detects that the aircraft has gained sufficient altitude that it is no
longer in the takeoff phase of flight.
Selecting flap override increases the allowable altitude loss as shown in Figure 1.3.1.3-1. This allows optional pattern work to
be performed without unwanted warnings. An additional biasing, or modifying of the envelope occurs above 700 feet AGL at
the rate of 5 feet additional altitude loss allowed per second.
If the aircraft penetrates the Mode 3 boundary, the aural message “Don’t Sink” is generated, and alert discretes are provided
for activation of visual annunciators. The visual annunciators remain active until a positive rate of climb is re-established.
1.3.1.4 Mode 4 - Unsafe Terrain Clearance
Mode 4 provides alerts for insufficient terrain clearance with respect to phase of flight and speed. Mode 4 exists in three
forms, 4A, 4B and 4C. Mode 4A is active during cruise and approach with gear not in landing configuration. Mode 4B is
also active in cruise and approach, but with gear in landing configuration. Mode 4C is active during the takeoff phase of
flight with either gear or flaps not in landing configuration.
As shown in Figures 1.3.1.4-1 the standard boundary for Mode 4A is at 500 feet radio altitude. If the aircraft penetrates this
boundary with the gear still up, the voice message will be “Too Low Gear”. The same boundary is used to produce a “Too
Low Flaps” message if this boundary is penetrated with flaps still up in fixed gear aircraft. Above 178 knots, the boundary
increases linearly with airspeed to a maximum of 750 feet radio altitude at 200 knots or more. An alternate airspeed
expansion range, activated by a configuration item in the configuration module, begins at 148 knots and ends at 170 knots for
slower aircraft. Penetrating this boundary produces a “Too Low Terrain” message.