Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 16
"TOO LOW
TERRAIN"
"TOO LOW TERRAIN"
MODE 4B UNSAFE TERRAIN
CLEARANCE
"TOO LOW FLAPS"
AIRCRAFT SLOWED TO
LESS THAN 150 KTS
RUNWAY
0 100 200 300 400
UNSAFE TERRAIN CLEARANCE
COMPUTED AIRSPEED (KTS)
M
IN
T
E
R
R
A
IN
C
LE
A
R
A
N
C
E
(F
T
)
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
GEAR DN, FLAPS UP
TOO LOW FLAPS
WARNING AREA
TOO LOW TERRAIN
WARNING AREA
GEAR DOWN
FIGURE 1.3.1.4-3: MODE 4B - UNSAFE TERRAIN CLEARANCE - GEAR DOWN (TURBOPROP)
The Mode 4B curve associated with turbofan aircraft is available on the MKVIII EGPWS. When the landing gear is lowered,
this mode becomes active and the boundary decreases to 245 feet. Penetration below 159 knots results in the “Too Low
Flaps” message with gear down and flaps not in landing configuration, while above 159 knots the message is “Too Low
Terrain”. Mode 4B is illustrated in Figure 1.3.1.4-4.
"TOO LOW
TERRAIN"
"TOO LOW TERRAIN"
MODE 4B UNSAFE TERRAIN
CLEARANCE
"TOO LOW FLAPS"
AIRCRAFT SLOWED TO
LESS THAN 159 KTS
RUNWAY
0 100 200 300 400
UNSAFE TERRAIN CLEARANCE
COMPUTED AIRSPEED (KTS)
M
IN
T
E
R
R
A
IN
C
LE
A
R
A
N
C
E
(F
T
)
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
GEAR DN, FLAPS UP
TOO LOW FLAPS
WARNING AREA
TOO LOW TERRAIN
WARNING AREA
GEAR DOWN
FIGURE 1.3.1.4-4: MODE 4B - UNSAFE TERRAIN CLEARANCE - GEAR DOWN (TURBOFAN)
Mode 4C is based on a minimum terrain clearance, or floor, that increases with radio altitude during takeoff. A value equal to
75% of the current radio altitude is accumulated in a long-term filter. Any decrease of radio altitude below the filter value
with gear or flaps up will result in the warning “Too Low Terrain”. Mode 4C for turboprops is illustrated in Figure 1.3.1.4-5,
and Mode 4C for turbofans is illustrated in Figure 1.3.1.4-6.