Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 67
AIRSPEED (KTS)
ALERT AREA
EXPANDED
ALERT
AREA
30 FT
170 KTS
750 FT
0 100 200 300
118 KTS
150 FT
M
IN
T
E
R
R
A
IN
C
LE
A
R
A
N
C
E
(F
T
)
1000
800
600
200
0
400
FIGURE 6.2.4.1-8: MODE 4B STATIC ALERT ENVELOPE (ALTERNATE AIRSPEED RANGE, MODE TYPE 9)
6.2.4.2 Mode 4C
Mode 4 also provides an alert based on minimum radio altitude clearance during takeoff as illustrated in Figure 6.2.4.2-1.
This alert is similar to the Mode 4A alert that is active during the cruise and approach phases of flight, only in this case, the
minimum terrain clearance is a function of the radio altitude of the aircraft. The sloped portion of the envelope boundary is
described by the equation:
MIN TERRAIN CLEARANCE (FT) = 0.75 [RADIO ALTITUDE (FT)]
Figure 6.2.4.2-1 is a block diagram of Mode 4C. The actual Mode 4C envelopes are shown in Figures 6.2.4.2-2 through -3A.
RADIO ALTITUDE
LANDING GEAR
LANDING FLAPS
TAKEOFF MODE
MODE 4 LIMIT
AIRSPEED
MODE 4C ALERT
MODE 4C
ENABLE
MODE 4
FLOOR
GENERATOR
LIMITER
MAX
MAX
X
Y
X
Y
C<B
B
C
M
O
D
E
4
C
E
N
A
B
L
E
L
O
G
I
C
IN AIR
RADIO ALTITUDE
RADIO ALTITUDE
FLAPS OR GEAR UP
TAKEOFF MODE
FIGURE 6.2.4.2-1: MODE 4C BLOCK DIAGRAM