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through using a combination of MAX gain and tilt control. Setting the tilt
to zero and the gain to MAX may allow the radar to see the ice crystals
that compose the top of the thunderstorms (figure 4-71). If ANY weather
is detected in front of the aircraft, then adjust the tilt downward to see if
the weather return grows in intensity (figure 4-72). If it does, you can
be fairly sure that you are approaching the glaciated (composed of ice
crystals) top of a thunderstorm cell.
Figure 4-71 shows the aircraft at 39,000 feet with tilt set to zero degrees.
Gain is set to MAX. A minimal weather return shows at 25 NM.
1st Edition, 1st Revision
18 Sep 03 4-73
MULTISCAN OPERATION COLLINS
MultiScan Manual Operation MultiScan™ Radar
Figure 4-71 TILT Set to Zero, GAIN Set to MAX: Minimal Weather
Return
Figure 4-72 shows the aircraft at 39,000 feet with tilt set to -7° and gain
set to MAX. A strong weather return at 25 NM indicates significant
convective activity that more than likely will cause turbulence when the
aircraft passes this point.
1st Edition, 1st Revision
4-74 18 Sep 03
COLLINS MULTISCAN OPERATION
MultiScan™ Radar MultiScan Manual Operation
Figure 4-72 TILT Set to -7°, GAIN Set to MAX: Strong Weather Return
Due to the fact that the beam diameter increases with range (♦page
6-20), this method is most accurate when the storm cell is within 40
NM of the aircraft. Once weather is detected with the 0° tilt setting,
significant down tilt will be required to look below the aircraft flight path
to investigate for thunderstorm activity.
1st Edition, 1st Revision
18 Sep 03 4-75
MULTISCAN OPERATION COLLINS
MultiScan Manual Operation MultiScan™ Radar
CAUTION
Method four can give indications of possible turbulence in the
aircraft flight path but should be used in conjunction with methods
1, 2 or 3 in order to prevent missing significant weather that is below
the radar beam but still a turbulence threat.
STORM HEIGHT ESTIMATION (RADAR TOP ONLY)
WARNING
Although the following formula is valid for estimating the wet tops
of storm cells within 100 miles, pilots should be aware that the
weather radar will not “paint” frozen dry top precipitation such as
snow or hail (due to low reflectivity). These low reflectivity targets
are frequently accompanied by severe turbulence. This fact should
be taken into account – for this reason it is not recommended that
pilots attempt to overfly or underfly storm cells.
The height of the radar top or wet top (♦page 5-5) of a thunderstorm
can be estimated by raising the tilt until the storm disappears from the
radar display (figure 4-73). Height is then equal to the aircraft altitude
+ (antenna tilt x distance x 100).
WARNING
The top of the precipitation activity is not necessarily the top of the
danger area. Dangerous turbulence frequently exists at altitudes
significantly above the altitude at which detectable precipitation
is formed.
In figure 4-74, the tilt is raised until the storm cell has all but disappeared
when 2° up tilt has been selected. The cell is 25 NM in front of the
aircraft and the aircraft is at 30,000 feet. Therefore, the estimated height
of the wet top of the storm is at 3,500 feet. Remember that significant
vertical thunderstorm development and associated turbulence may exist
above the wet top of a thunderstorm.
1st Edition, 1st Revision
4-76 18 Sep 03
COLLINS MULTISCAN OPERATION
MultiScan™ Radar MultiScan Manual Operation
Figure 4-73 Using Tilt to Estimate Radar Top of Thunderstorm
1st Edition, 1st Revision
18 Sep 03 4-77
MULTISCAN OPERATION COLLINS
MultiScan Manual Operation MultiScan™ Radar
Figure 4-74 Radar Display of Storm Top
1st Edition, 1st Revision
4-78 18 Sep 03
COLLINS MULTISCAN OPERATION
MultiScan™ Radar MultiScan Manual Operation
CAUTION
Significant vertical thunderstorm development and corresponding
severe turbulence may exist above the radar/wet top of a
thunderstorm (♦page 5-5).
LONG RANGE (OVER THE HORIZON)WEATHER DETECTION
The ability to gather strategic weather information out to 320 NM is
possible if proper tilt procedures are utilized. First one must realize that
over a distance of 320 NM the curvature of the earth causes the earth’s
surface to fall away by approximately 65,000 feet. Thus, if the aircraft
is at 25,000 feet at its current position, the earth’s surface is actually
90,000 feet below the aircraft at 320 NM distance. If common practice
is followed and the tilt is adjusted to eliminate the majority of ground
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Collins Weather Radar operator’s guide(25)
