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problem at low and mid altitudes, the problem becomes a significant
threat at high cruise altitudes. Many pilots use tilt settings based
on the 80 NM range scale during high altitude cruise. However, at
high altitudes this setting only optimizes weather returns between
approximately 50-80 NM. Significant weather may be present in the 0-50
NM area. Over-scanning and subsequent inadvertent thunderstorm
top penetration is a significant concern. Targets inside 50 NM may be
over-scanned and disappear from the display but still cause significant
turbulence. To view targets inside the 50 NM range, large down tilt
settings are necessary. The large down tilt may prevent more distant
storms from being detected, and in overland operations, will cause
excessive ground clutter to appear.
N NOTE
Several pilot techniques that can be used to avoid over-scanning
threat weather can be found in the Over-Scan Prevention
Techniques section on ♦page 4-72.
WARNING
Over-scanning and the resulting inadvertent thunderstorm top
penetration is a significant threat during high altitude operations. N NOTE
MultiScan’s lower beam is adjusted to hold significant weather in
the radar beam far longer than conventional radars. In addition,
OverFlight™ protection incorporates a memory feature to ensure
that any thunderstorm that is a threat to the aircraft will remain on
the display until it passes behind the aircraft.
1st Edition, 1st Revision
18 Sep 03 4-71
MULTISCAN OPERATION COLLINS
MultiScan Manual Operation MultiScan™ Radar
RECOMMENDED TILT SETTINGS FOR OVER WATER
OPERATION
The table below provides recommended tilt settings for aircraft operating
over water when ground clutter is not available to help determine the
optimum tilt angle. The recommended tilt settings place the lower part
of the antenna beam at the edge of the outer range scale.
Recommended Over Water Tilt Settings
Altitude
(feet)
40 NM 80 NM 160 NM
40,000 -7° -3° -2°
35.000 -6° -2° -1°
30,000 -4° -1° 0°
25,000 -3° -1° 0°
20,000 -2° 0° +1° N NOTE
Lower tilt settings may be required due to the non-reflective nature
of oceanic weather (♦page 5-16).
OVER-SCAN PREVENTION – PILOT TECHNIQUES
Method 1: One pilot technique that is used to judge which storms are a
threat and which are not when using the 80 NM range scale is to use the
40 NM range (the mid point on the display) for a decision point criteria. If
the storm stays in the radar beam (i.e., is painted on the display) through
40 NM, then it should be considered a potential threat and avoided.
Thus, a storm cell that disappeared from the display at 40 NM is still a
potential threat. The position should be tracked mentally and avoided.
Method 2: For aircraft equipped with a split function control panel
(♦page 4-2), another technique can be used to reduce the threat of
over-scanning significant weather. In this case one pilot should utilize
the 80 NM range scale (or higher) with a tilt setting that places ground
clutter in the outer most range scale while the second pilot utilizes a 40
NM range (or less) with an increased down tilt that places clutter in
the outer range scale of the 40 NM display. Use suggested mid and
high altitude tilt settings over water when ground return is not present.
1st Edition, 1st Revision
4-72 18 Sep 03
COLLINS MULTISCAN OPERATION
MultiScan™ Radar MultiScan Manual Operation
The 80 NM range is then available to help plan any required course
changes and the shorter range can be used to prevent over-scanning
and inadvertent thunderstorm top penetration.
The left picture shows the radar display with the aircraft at 35,000 feet
with 40 NM range selected. The picture on the right shows the radar
display at the same altitude, but with 80 NM range selected. Note the
cell directly in the aircraft path that has disappeared from the 80 NM
range scale.
Figure 4-70 Radar Displays Using Split Function
Method 3: The threat of over-scanning can be reduced by periodically
selecting the 40 NM range scale and adjusting the tilt so that some
clutter appears in the outer most range scale. Observe potential target
threats in this region. Then switch to the 80 NM range scale and adjust
the tilt upwards until ground clutter is once again in the outer range
scale only. Continue adjusting the range and tilt until the desired range
scale is in use. Repeat the procedure periodically or when the location
of thunderstorms within 40 NM of the aircraft needs to be determined.
Method 4: Another way to detect possible impending turbulence is
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Collins Weather Radar operator’s guide(24)
