Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 84
The algorithm as shown in figure 6.5.1-2 calculates a total windshear indication and does not resolve individual horizontal
and vertical windshear components. The shear signal is modulated by radio altitude and roll angle in order to provide further
margin against unwanted alerts that could potentially result from turning into and out of winds.
NORMAL
ACCELERATION
ALTITUDE
TRUE
AIRSPEED
DIVIDE
A/B
A
B
+
+
+
+
-
LOW PASS
FILTER
+
-
RADIO ALTITUDE
SHEAR
GAIN
CONTROL
FUNCTION
FILTERED SHEAR
ROLL
ATTITUDE
GAMMA
MULTIPLY
(AIR MASS AXIS)
LONGITUDINAL
ACCELERATION
(AIR MASS AXIS)
LOW PASS
FILTER
-
RATE
7BLKWSC1 5-13-92 BCB
K
LIMITER
+/- K2 G's
LONG TERM
ERROR
INTEGRATOR
LIMITER
+/- K1 G's
FIGURE 6.5.1-2: WINDSHEAR COMPUTATION DIAGRAM
The shear value is then compared to thresholds that are a function of aircraft type to determine an excessive windshear
condition. The thresholds are modulated as a function of static air temperature, excess lift above Vref (during approach), and
flight path angle. This modulation provides improved immunity against turbulence-induced nuisance alerts and advanced
recognition of microburst windshear events. Figure 6.5.1-3 shows a typical windshear threshold for caution and warnings.
Once the modulated threshold has been exceeded, a siren is sounded, followed by the voice aural “Windshear Windshear
Windshear” (or equivalent). This message is given only once, provided the aircraft does not exit and re-enter the windshear
detection envelope or the external command is not re-activated after an 8 second lockout.
An output warning lamp is also activated upon exceeding the windshear threshold. This lamp remains on as long as the shear
condition exists, or as a minimum, 8 seconds.
The other GPWS modes are inhibited for a minimum of 5 seconds after a windshear warning. These modes may also be
inhibited within 60 seconds after a windshear warning through activation of the escape guidance aural inhibit signal. This
signal can come from a digital or discrete source.