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use airspace. If the special use airspace is a Class B, Class C, CTA, or
TMA, the message page will also instruct you to see the Airport 4 page
(airport communications) for the primary airport so that the correct com-
munications frequency may be determined.
The SUA alert feature is three dimensional. The SUA areas are stored in
the KLN 90B database with regard to altitude when the actual SUA alti-
tude limitations are charted in terms of mean sea level (MSL). Therefore,
if you are flying either above or below an SUA area you won’t be inconve-
nienced with nuisance alert messages. However, if the actual lower limit
of a SUA is charted in terms of an altitude above ground level (AGL), then
it is stored in the KLN 90B as all altitudes below the upper limit of the
SUA. If the actual upper limit of a SUA is charted in terms of AGL, it is
stored in the KLN 90B as “unlimited”.
If the altitude input to the KLN 90B is pressure altitude from an altitude
encoder or air data computer, then you must manually update the
KLN 90B with an altimeter setting (baro correction) in order to receive
accurate SUA alerting. You may easily update the altimeter setting by
pressing the A button to display the Altitude page. The cursor will be
over the inches field if “inches” was previously selected on the SET 7
page. If “millibars” was selected on the SET 7 page then the cursor will be
over the first two digits of the millibar field. The left inner knob is used to
change the digits and the left outer knob is used to move the cursor to the
desired position. When the altimeter setting is complete, press A to
return to the pages previously in view.
CAUTION: Failure to keep the altimeter setting updated will result in
inaccurate special use airspace alerting. If this feature is used, it is a
good idea to update the altitude setting on the ALT page each time
you make a change to a aircraft’s altimeter setting.
NOTE: If there is no altitude input to the KLN 90B, all altitudes will be
regarded as being within the boundary of the SUA area.
Only the outer lateral boundaries are stored for Class B, Class C, CTAs,
and TMAs. These SUA areas are stored as “cylinders” of airspace so all
altitudes below the upper limit of these areas are considered to be in the
SUA.
The message prompt for a special use airspace alert will occur when the
aircraft’s position is at a point such that a projection of the aircraft’s
existing track over the ground is approximately 10 minutes from pene-
trating the outer boundary of one of these areas. It will also occur if the
aircraft is within approximately two nautical miles of one of these areas
even if the aircraft’s projected track over the ground won’t actually pene-
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