Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 50
The static Mode 1 inner curve for turbofan airplanes (available on MKVIII EGPWS only) is composed of two straight lines
with the equations:
(lower line) RADIO ALTITUDE (FT) = -1620 (FT) - 1.1133 * ALTITUDE RATE (FPM)
(upper line) RADIO ALTITUDE (FT) = -400 (FT) - 0.4 * 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
h
o
u
sa
n
d
s)
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
2450 FT
-7125 FPM
284 FT
-1
7
1
0
F
P
M
-1
4
8
2
F
P
M
10 FT
WARNING AREA
FIGURE 6.2.1-3A: MODE 1 INNER CURVE (TURBOFAN)
During normal conditions, the system will base Mode 1 computations upon barometric rate from the ADC. If this computed
data is not valid or available then the system will use internally computed barometric altitude rate.
The presence of ground effect on the barometric rate data prevents its use close to the ground due to the potential for nuisance
warnings. Consequently, Mode 1 is cut off at 50 feet radio altitude. Mode 1 is cut off at 10 feet radio altitude for turbofan
aircraft.
The outer curve is effective below a radio altitude of 2450 feet. The inner curve is effective below a radio altitude of 1958
feet for Turboprop aircraft and 2450 feet for turbofan aircraft.
There is a 0.8 second delay for the "Sinkrate" caution to minimize nuisance alerts caused by momentary penetration of the
outer envelope. There is a delay for the "Pull Up" warning to guarantee that at least one "Sinkrate" (or equivalent) message
will be given before the "Pull Up" message starts.