Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 47
6.2.1 Mode 1 -- Excessive Descent Rate
Mode 1 provides an alert based on valid radio altitude and valid aircraft descent rate. The descent rate is computed based on
barometric rate from the Air Data Computer (ADC). Two different alert envelopes are possible. Through Envelope
Modulation, both envelopes can be biased to the right at certain airports to minimize nuisance alerts. Figure 6.2.1-1 illustrates
Mode 1 functionality.
DELAY
0.8 SEC
0.2 SEC
ALTITUDE
RATE
(FPM)
RADIO
ALTITUDE
(FT)
X
Y
X
Y
X
Y
CAUTION LAMP
COMPARATOR
TIME TO IMPACT
COMPARATOR
WARNING
COMPARATOR
X
X
X
Y
Y
Y
SINKRATE
VOICE
CONTROL
LOGIC
DELAY
Note 1
0.2 SEC
MODE 1
SINKRATE
LAMP
MODE 1
SINKRATE
VOICE
MODE 1
PULL UP
FLAP OVERRIDE OR
ENVELOPE
MODULATION OR
STEEP APPROACH OR
GLIDESLOPE
DEVIATION BIAS
FLAP OVERRIDE OR
ENVELOPE
MODULATION OR
STEEP APPROACH OR
GLIDESLOPE
DEVIATION BIAS
VOICE/LAMP
Note 1: No delay if Sinkrate occurred.
FIGURE 6.2.1-1: MODE 1 BLOCK DIAGRAM
Figure 6.2.1-2 illustrates the static alert envelope for the Mode 1 outer envelope for turboprop airplanes, which is typically the
"Sinkrate" warning area. The curve for turbofan airplanes is similar, but it extends down to 10 feet as shown in Figure 6.2.1-
2A. This static alert envelope assumes that all signals are generated instantaneously (i.e. no filter lags or time delays), and
that the bias terms are zero.
The static Mode 1 outer curve is a straight line with the equation:
RADIO ALTITUDE (FT) = -572 (FT) - 0.6035 * ALTITUDE RATE (FPM)