Technical data
Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 15
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
TOO LOW GEAR
WARNING AREA
TOO LOW TERRAIN
WARNING AREA
GEAR UP, FLAPS UP
"TOO LOW
TERRAIN"
"TOO LOW TERRAIN"
MODE 4A UNSAFE TERRAIN
CLEARANCE
"TOO LOW GEAR"
AIRCRAFT SLOWED TO
LESS THAN 178 or 148 KTS
RUNWAY
FIGURE 1.3.1.4-1: MODE 4A - UNSAFE TERRAIN CLEARANCE - GEAR UP (TURBOPROP)
Mode 4 curves with specific application for turbofan aircraft are available on the MKVIII EGPWS. As shown in Figures
1.3.1.4-2 the standard boundary for Mode 4A for this curve 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 190 knots the boundary
increases linearly with airspeed to a maximum of 1000 feet radio altitude at 250 knots or more. Penetrating this boundary
produces a “Too Low Terrain” message.
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
TOO LOW GEAR
WARNING AREA
TOO LOW TERRAIN
WARNING AREA
GEAR UP, FLAPS UP
"TOO LOW
TERRAIN"
"TOO LOW TERRAIN"
MODE 4A UNSAFE TERRAIN
CLEARANCE
"TOO LOW GEAR"
AIRCRAFT SLOWED TO
LESS THAN 190 KTS
RUNWAY
FIGURE 1.3.1.4-2: MODE 4A - UNSAFE TERRAIN CLEARANCE - GEAR UP (TURBOFAN)
When the landing gear is lowered, Mode 4B becomes active and the boundary decreases to 170 feet for turboprop aircraft.
This is reduced to 150 feet on those aircraft types that routinely delay full flap deployment until the airfield is within
approximately one nautical mile (enabled by a configuration item in the configuration module). In addition, an optional curve
(enabled by a configuration item in the configuration module) places the upper boundary at 200 feet. Penetration below 150
knots results in the “Too Low Flaps” message with gear down and flaps not in landing configuration, while above 150 knots
the message is “Too Low Terrain”. Mode 4B is illustrated in Figure 1.3.1.4-3.