Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 49
For some installations a steep approach bias can be optionally applied to the Mode 1 curves. If steep approach is enabled and
the steep approach discrete is selected, then fixed positive biases are added to both the Sinkrate curve (500 FPM), and the
Pull Up curve (200FPM). If steep approach is activated, then the cockpit self test is inhibited when the aircraft is on the
ground. The selected Discrete I/O category ID will provide either an alternate action Steep Approach switch input, or a
momentary type switch input. The momentary type provides an automatically resetting Steep Approach function. Pressing the
switch once will activate Steep Approach. It can be cancelled by pressing the switch again, or will automatically reset when
the aircraft lands, or flaps/gear raised for a go-around. Use of the momentary switch requires that it be illuminated by the
Steep Approach Lamp discrete output. This lamp is also activated if Envelope Modulation activates a Steep Approach.
Penetration of the outer envelope will activate the caution lamps (or warning lamps if using Lamp Format 1) and produce the
voice message "Sinkrate".
The audio message for penetration of the outer envelope will be repeated twice, then will remain silent unless the excessive
descent rate condition degrades by approximately 20%, as determined by the computed time to impact (i.e. radio
altitude/altitude rate). If 20% degradation in time to impact is computed, then additional two messages are given and the
cycle repeats. This situation will continue until the outer envelope is exited or until the Mode 1 inner envelope is penetrated.
It is important to note that using constant time to impact as the condition for holding the voice messages off assures that the
flight profile must be correcting toward lower descent rates at lower altitudes AGL. If the profile is not corrected, the voice
messages will continue to repeat getting closer and closer together as radio altitude is lost. The Mode 1 caution/warning lamp
output remains active so long as the excessive descent rate conditions exists.
During the time that the voice message for the outer envelope is inhibited and the caution/warning lamp is on, the Mode 5
alert message is allowed to annunciate for excessive glideslope deviation conditions. No additional lamps will come on. This
provides additional information to the flight crew in that not only are they descending too rapidly, but also their flight profile
has taken them below the glideslope beam.
Further penetration of the outer envelope will reach the inner envelope. The static envelope for this inner Mode 1 envelope is
illustrated in Figure 6.2.1-3, again assuming the bias term is zero. Here the voice warning will change from "Sinkrate" to
"Pull Up" and the caution lamps will change to warning lamps if using Lamp Format 2. The static Mode 1 inner curve for
turboprop airplanes (available on both MKVI and MKVIII EGPWS) is composed of two straight lines with the equations:
(lower line) RADIO ALTITUDE (FT) = -1625.47 (FT) - 1.1167 * ALTITUDE RATE (FPM)
(upper line) RADIO ALTITUDE (FT) = - 0.1958 * ALTITUDE RATE (FPM)
0 -2 -4 -6 -8 -10
(Thousands)
ALTITUDE RATE (FPM DESCENT)
M
IN
T
E
R
R
A
IN
C
L
E
A
R
A
N
C
E
(F
T
)
(T
housands)
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1958
FT
-10000
FPM
346
FT
-1765
F
P
M
-1500
F
P
M
50 FT
PULL UP
WARNING
AREA
FIGURE 6.2.1-3: MODE 1 INNER CURVE (TURBOPROP)