Select page 2 of STAT. Check almanac age
(ALM). If greater than 5000 hours, force a cold
periodically check STAT page 1 for SAT 3 or
SAT 4 message. Figure of merit (FM) is
another indication of a converging position fix
and can be directly monitored from page 1 of
any data selection, where FM alternates with the
system map datum and other alerts.
10. SAT 3 or SAT 4 should be displayed within five
minutes. If not, check that position, time, track,
and groundspeed have been entered correctly.
Also check that satellites are available. If all
available, force a cold start.
(b) GPS Quick Start.
Mode selector switch - Set to NAV directly from
OFF. After power-on test has been completed,
the GPS uses velocity estimates from the
aircraft's sensors (if available). If velocity is not
available from the aircraft, zero velocity is
assumed. If position and time are not available
from the aircraft, the position estimate from
GPS memory is used, and the internal low
power time source (LPTS) is uses to initialize
As the GPS is acquiring satellites, position,
time, and velocity estimates can be checked to
ensure that they are within start-up error limits.
If so, monitor STAT page 1. If not, a normal
start is required.
After SAT 4 is achieved with good EPE
(estimated position error), and FM (figure of
merit) of FM3 or below, check position, velocity,
GPS is now ready for normal navigation.
(c) GPS Cold Start.
Mode selector switch - INIT.
Data selector switch - OPT.
Slew key - Select page 4.
Enter 04 on line 1.
Line select key 2 - Press next to COLD START
Line select key 3 - Press next to COLD START
to clear cold start message and resume normal display.
Mode selector switch - NAV.
CHAALS Use of GPS and INS.
(1) CHAALS Concept. CHAALS (Coherent
High Accuracy Airborne Location System), is an emitter
location system that provides timely, high accuracy
locations required for targeting and to support emitter
CHAALS provides this capability through coherent
processing of differential doppler (DD) and time
difference of arrival (TDOA) information received at a
ground facility from the aircraft. CHAALS receivers
aboard the aircraft will receive and digitize emitter
signals. The data will be transmitted over the data link
to the GR/CS integrated processing facility (IPF).
There, CHAALS processors will perform the required
computations to produce accurate emitter locations.
The precise navigation required will be provided by the
positioning system (GPS). GPS also provides the
primary means of time synchronizing the CHAALS
receivers (signal conditioners or SC's) aboard the
aircraft. A backup for the GPS will be provided by the
data link. The resultant emitter reports will be sent to
GR/CS by CHAALS.
(2) GPS (and INS) Involvement. The accurate
and timely navigation (position and velocity) is provided
by integrating an INS with a GPS, and integrating both
(through a series of intermediaries) with a CHAALS
ground based navigation processor (NP). The SC, data
link, and CHAALS HSSP (high speed signal processor)
form the communication link. The critical airborne
synchronization include the following:
INS to GPS:
INS to CHAALS: Same as INS to GPS
GPS to CHAALS:
Navigation data block (position,
velocity, and time)
Error state vector data block (9
element ESV, time)
TM/covariance data block (time, TM