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3-17
Rev 1
3.6 INITIALIZATION AND TIME TO FIRST
FIX
Since the KLN 90B stores its position and other required
parameters in memory when power to the unit is
removed, it is seldom necessary to aid the unit in reach-
ing a NAV ready condition. The time required from power
on until the KLN 90B determines its present position and
is therefore ready to navigate is called “time to first fix.”
The time to first fix is normally a few minutes or less. In
order for the KLN 90B to reach a NAV ready condition, it
is necessary to meet the following conditions:
1.The KLN 90B’s “almanac” data must be current.
Almanac data is crude orbital information for all the
satellites and is used for initial acquisition when the
KLN 90B is first turned on. This data is stored in the
KLN 90B’s non-volatile memory and is considered cur-
rent for up to six months. Each satellite sends
almanac data for all satellites. Since the KLN 90B
routinely updates the almanac data during normal
operation, the almanac data will become out of date
only if the KLN 90B hasn’t been used for the previous
six months or longer. Collecting new almanac data
takes place automatically if the data is more than six
months old. If the almanac data is out of date and
needs to be collected, the KLN 90B will take a few
minutes to acquire your present position (usually
about six (6) minutes, but not more than 12 minutes).
The Self Test and Database pages should be
approved.
2.The aircraft must be located such that the GPS
antenna has an unobstructed view of the sky so that
required satellite signals are not being blocked. If
necessary, position the aircraft away from hangars or
other obstructions.
3.It is very helpful for the KLN 90B to have the correct
time, date and position to be able to determine which
satellites should be in view. This information is stored
in the battery backed memory of the KLN 90B so it is
not normally required to update it. If the KLN 90B has
the correct time, date and position, then the time to
first fix will usually be less than two (2) minutes. If this
information is not correct, then the KLN 90B will start
to look for any satellites. Eventually, the KLN 90B will
find enough satellites to determine the position of the
aircraft. This process can take as long as 12 minutes.
It is possible for you to update this information
manually which will allow the KLN 90B to reach a NAV
ready status much faster. To set the time and date
follow steps 6 and 7 in section 3.2, “Turn-On and Self-
Test.” If it is necessary to update the position then use
the following steps. Remember, if acquisition time is
not important then it is not necessary to update the
time, date or position.