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tendency is then to reduce power (figure 5-24). In this example, the
power has been reduced to zero pounds thrust.
Figure 5-24 Windshear Example — Power Reduction
1st Edition, 1st Revision
5-28 18 Sep 03
COLLINS AVIATION WEATHER
MultiScan™ Radar Microbursts And Windshear
The extreme danger point during a windshear event is when the aircraft
passes through the center. At this point (figure 5-25), the 40-knot
headwind turns very rapidly into a 40-knot tailwind so that indicated
airspeed suddenly drops from 170 knots to 90 knots. Power is still zero
and approach altitude has decreased to 200 meters. The aircraft is
now low, slow, and without power.
Figure 5-25 Windshear Example — Indicated Airspeed Transition
1st Edition, 1st Revision
18 Sep 03 5-29
AVIATION WEATHER COLLINS
Microbursts And Windshear MultiScan™ Radar
If there is sufficient time and altitude and if the windshear is not
overly severe, addition of power may allow the crew to fly through the
windshear event. However, recovery from the windshear event and
associated actions described in this example would be unlikely (figure
5-26).
Figure 5-26 Windshear Event — Recovery or Loss of Flight
WARNING
Windshear resulting from a microburst can be an extreme hazard
during take off and landing.
1st Edition, 1st Revision
5-30 18 Sep 03
COLLINS AVIATION WEATHER
MultiScan™ Radar Hazardous Weather
HAZARDOUS WEATHER
INTRODUCTION
A normal thunderstorm is circular or oval in shape (figure 5-27).
Variations from this normal shape are indicative of a shear condition
within the thunderstorm and can serve as clues to hazardous weather
(figure 5-28).
Figure 5-27 Normal Thunderstorm Shape
1st Edition, 1st Revision
18 Sep 03 5-31
AVIATION WEATHER COLLINS
Hazardous Weather MultiScan™ Radar
Figure 5-28 Shear Conditions within Thunderstorm Shape
1st Edition, 1st Revision
5-32 18 Sep 03
COLLINS AVIATION WEATHER
MultiScan™ Radar Hazardous Weather
STEEP GRADIENT
A steep gradient occurs when the green and yellow portions of the
thunderstorm shown on a weather radar display merge very rapidly into
red (figure 5-29). A steep gradient is indicative of significant convective
activity and heavy turbulence.
Figure 5-29 Steep-Gradient Thunderstorm
The circled thunderstorm in figure 5-29 has a steep gradient because
the green and yellow portions of the cell quickly move to red. A steep
gradient is indicative of extensive convective activity, and severe
turbulence would more than likely be encountered if the aircraft
penetrated the thunderstorm.
1st Edition, 1st Revision
18 Sep 03 5-33
AVIATION WEATHER COLLINS
Hazardous Weather MultiScan™ Radar
SCALLOPED EDGES, PENDANT, FINGER, HOOK,
U-SHAPE
Scalloped or roughened edges (figure 5-30), pendants (figure 5-31),
fingers (figure 5-32), hooks (figure 5-33), and U-shapes (figure 5-34) on
weather radar thunderstorm displays all indicate the presence of sheer
forces and turbulence. They may also indicate the presence of hail.
WARNING
Increase the avoidance distances by 50 percent for echoes that
are changing shape rapidly or are exhibiting hooks, fingers, or
scalloped edges.
Figure 5-30 Thunderstorm Showing Scalloped Edges
1st Edition, 1st Revision
5-34 18 Sep 03
COLLINS AVIATION WEATHER
MultiScan™ Radar Hazardous Weather
Figure 5-31 Thunderstorm Showing Pendants
Figure 5-32 Thunderstorm Showing Fingers
1st Edition, 1st Revision
18 Sep 03 5-35
AVIATION WEATHER COLLINS
Hazardous Weather MultiScan™ Radar
Figure 5-33 Thunderstorm Showing A Hook
Figure 5-34 Thunderstorm Showing A U-Shape
1st Edition, 1st Revision
5-36 18 Sep 03
COLLINS AVIATION WEATHER
MultiScan™ Radar Non-Reflective Weather
NON-REFLECTIVE WEATHER
Stratiform clouds and small cumulous cloud buildups often do not
contain enough moisture to reflect radar energy (♦page 6-4). Note that
even though small cumulous cloud buildups that resemble popcorn
or cotton balls (figure 5-35) seldom reflect radar energy, they are still
associated with light to moderate turbulence.
Figure 5-35 Popcorn-Shaped Cumulous Cloud Buildups
1st Edition, 1st Revision
18 Sep 03 5-37
AVIATION WEATHER COLLINS
Non-Reflective Weather MultiScan™ Radar
These popcorn-shaped clouds are formed when warm moist air rises,
then cools to the dew point. When this occurs, the air is saturated with
moisture and a cloud forms. The clear air spaces between these clouds
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Collins Weather Radar operator’s guide(33)
