Honeywell SPZ-8000 Maintenance Manual page 275

The navigation computer also has input capability for three long range
sensors through ARINC 429 interfaces. The navigation computer can accept
two more long range
sensors through the
ASCB interface for a total
capability of five
sensor inputs. These
sensors will typically be three
IRS sensors, though Omega or GPS sensors can be substituted in place of
IRS units. These
long range sensors are utilized
in addition to
VOR/DME/DME inputs for overland flight. The IRS, GPS, and Omega/VLF
inputs are the only navigation source inputs utilized when VOR/DME
signals are not receivable. The navigation computer will automatically
choose the best navigation combination (VOR/DME, IRS, Omega, GPS) based
on predefined priority. When using VOR/DME inputs, a blending of these
inputs and IRS and GPS information occurs. This blending is done via
complementary filtering. Filtering lessens the effects of error and noise
in both the VOR/DME, IRS, and GPS inputs and, thus, provides a smooth and
accurate position derivation.
NOTE " GPS blending was activated in the -976 NAV computer and is for
'" display only in the -963, -964, and -978 Navigation Computers.
The navigation computer provides automatic tuning of the aircraft VOR and
DME receivers. Calculation of aircraft present position from VOR/DME
information requires input of bearing and distance and knowledge of the
station coordinates. The database is periodically used by the navigation
computer to find the coordinates and frequency of the high and low
altitude VORTAC and VOR/DME stations in the aircraft vicinity. When the
desired VOR and DME stations are chosen, the frequency is output to the
navigation receivers. Automatic receiver tuning is operationally
transparent to the pilot other than a periodic change in the receiver's
frequency display and the RMI pointer. Provision is included for remote
tuning of receivers via the CDU or manual tuning through the radio
control heads. For remote tuning via the CDU, the pilot can choose to
enter the station identifier or enter the frequency. The frequency of the
entered station found in the database is output to the navigation control
heads, then to the receivers. For manual tuning via the radio control
head, the navigation computer will input the frequency code from the
receiver and compare it to the frequencies of stations in the aircraft
vicinity. The frequency comparison will allow the navigation computer to
deduce what station is being tuned. A comparison of calculated bearing
and distance to input bearing and distance will resolve the remote
possibility of two or more stations in the aircraft vicinity transmitting
on the same frequency.
An important part of the navigation computer is the nonvolatile memory
area or database which contains information on navaids, airports, and
airways. The database is integral to the navigation computer to allow
quick access of the stored information. The database is reprogrammable
and is loaded with worldwide data. The worldwide data includes VOR,
VORTAC, VOR/DME, airport reference points, runway thresholds, and high
altitude airway intersections plus airway routes and SIDs/STARs
procedures. The navigation data requires updating on a 28-day cycle.
Updates are required due to changes in the data associated with each
station or airport. The database memory is also used to store pilot-
defined waypoints and pilot-defined routes; however these are not
updated every 28 days. They reside in memory until changed by the
operator.
22-14-00
Page 198.104
Apr 15/93
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