Bendix Commercial Vehicle Systems Bendix/King Global Positioning System KLN 35A - Manual (Page 53)

3.6. INITIALIZATION AND TIME TO FIRST FIX
Since the KLN 35A 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 reaching a NAV ready condition. The time required
from power on until the KLN 35A 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 35A to
reach a NAV ready condition, it is necessary to meet the following
conditions:
1. The KLN 35A’s “almanac” data should be current. Almanac data
is orbital information for all the satellites and is used for initial
acquisition when the KLN 35A is first turned on. This data is
stored in the KLN 35A’s non-volatile memory and is considered
current for up to six months. Each satellite sends almanac data
for all satellites. Since the KLN 35A routinely updates the
almanac data during normal operation, the almanac data will
become out of date only if the KLN 35A hasn’t been used for the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If the almanac data is out of date and needs to be collected, the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 35A will take a few minutes to acquire your present position
(usually about six (6) minutes, but not more than 12 minutes).
The Self Test, Initialization, and Data Base 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 possible, position the aircraft away from
hangars or other obstructions.
3. It is very helpful for the KLN 35A to have the correct time, date
and position to be able to determine which satellites should be in
view. This infomation is stored in the battery backed memory of
the KLN 35A so it is not normally required to update it. If the KLN
35A 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 35A will start to look for any satellites.
Eventually, the KLN 35A 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 35A to reach a NAV ready status much
faster. To set the time and date follow steps 5 and 6 in
section
3.2 , “Turn-On and Self-Test.” The initial position is usually set
during turn-on and self-test, but if for some reason it is necessary
Basic GPS Operation
3-18 Effective Date 5/95 006-08791-0000 Rev 0
Basic GPS Operation
Chapter 3