Garmin Appliance Data User's Guide download pdf (Page 113)

101190-00607-02 Rev D

Detailed Operation

Radar

MPEL

Boundary

Radome

Center Line of

Aircraft

10.83 ft for 12” ant

Antenna

MPEL Boundary

Antenna Tilt Setup at Cruise Altitude

The following discussion is a simple method for

setting up the weather radar antenna tilt for most situ-

ations. It is not to be considered an all encompassing

setup that will work in all situations, but this method

does provide good overall parameters for the monitor-

ing of threats.

With the aircraft ﬂying level, adjust the antenna

tilt so ground returns are displayed at a distance that

equals the aircraft’s current altitude (AGL) divided by

1,000. For example, if the aircraft is at 14,000 feet,

adjust the tilt so the front edge of ground returns are

displayed at 14 nautical miles. Note this antenna tilt

angle setting. Now, raise the antenna tilt 6 degrees

above this setting. The bottom of the radar beam is

now angled down 4 degrees from level.

At this point, when ﬂying at altitudes between

2,000 and 30,000 feet AGL, any displayed target

return should scrutinized. If the displayed target

advances on the screen to 5 nautical of the aircraft,

avoid it. This may be either weather or ground returns

that are 2,000 feet or less below the aircraft. Raising

the antenna tilt 4 degrees can help separate ground

returns from weather returns in relatively ﬂat terrain.

This will place the bottom of the radar beam level with

the ground. Return the antenna tilt to the previous

setting after a few sweeps.

NOTE: At aircraft altitudes under 5,000 feet AGL,

false returns are possible due to reﬂections from

side-lobe beams.

If the aircraft is above 29,000 feet, be cautious

of any target return that gets to 30 nautical miles or

closer. This is likely a thunderstorm that has a top high

enough that the aircraft cannot ﬂy over it safely.

If the aircraft altitude is 15,000 feet or lower, set

the displayed range to 60 miles. Closely monitor any-

thing that enters the display.

Also, after setting up the antenna tilt angle in

this manner, ground returns can be monitored for

possible threats. A ratio of approximately 100 to 1

exists between vertical distance from the aircraft and

horizontal distance. Therefore, at this antenna tilt

setting, a target return at 1 NM is approximately 400

feet below the aircraft; at 10 NM, 4,000 feet below; at

50 NM, 20,000 feet, etc. In other words, at this tilt set-

ting, a ground return (such as a mountain peak) being

displayed at 10 NM would have a maximum clearance

of 4,000 feet. If that ground target return moves to 5

NM, maximum clearance will be 2,000 feet.

This setup will provide a good starting point for

practical use of the GWX 68 Weather Radar System.

There are many other factors to consider in order to

become proﬁcient at using weather radar in all situa-

tions.

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Garmin Appliance Data User's Guide Page 113

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