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velocity may take as long as 25 minutes, this shouldonly
be attempted if serious INS degradation is suspected,
JTIDS is not available,a nd a reasonables ystemv elocity
is available. The preferred source of INS in-flight alignment
is JTIDS. A JTIDS in-flight align with good quality
JTIDS velocity data should align in 12 to 15 minutes
(display of an ALIGN COMPLETE message).
The quality of the air data velocity will depend upon
the accuracy of entered or available wind information.
System velocity is the computed optimum velocity using
all available inputs. JTIDS velocity data is computed
by the JTIDS system and is dependent on data
received from the MCS and over the link.
Since an INS in-flight align uses current system position
information, it is desirable to perform a one-fix
position update prior to performing an INS in-flight
align.
The procedure for in-flight align is as follows:
1, Verify a valid source of true heading is available,
such as SAHRS by selecting SAHRS on the upper
right portion of the OWN A/C MFD format. If a
reasonable SAHRS true heading is not available,
then enter the best estimated trne heading via the
DEU OWN A/C format (Figure 20-23).
2. Advance the NAV MODE switch to the IFA position.
The IFA MFD format shown in Figure 20-23
will appear.
3. Select a velocity source by depressing a pushbutton
on the right side of the IFA MFD format.
NAVAIR Ol-F14AAD-1
4. Observe the alignment progress on the IFA MFD
format.
5. To ensure a good initial platform alignment, flight
should be straight and level from 1 to 5 minutes. I
Note
Because of the extensive time required for
INS IFA, it is possible to select the INS mode
via the NAV MODE switch prior to an INS
align completem essageA. t this time the INS
may advance to the inertial mode or may
operate in the ATT mode, depending upon
the alignment progress at the time.
20.3.5.2 Secondary Navigation. The secondary
navigation mode uses SAHRS-sensed dynamic inputs,
with the SAHRS in its normal operating mode, as well
as inputs from the CADC and other aid sources, when
selected and available. This mode will be automatically
selected when the INS primary mode is not available
because of either an INS failure or INS operation in a
degradedm ode (i.e., ATT mode). Indication of this condition
can be observed on the MFD OWN A/C format,
that will show SAHR boxed in the upper right portion
and only SAHRS appearing as the legend in the center
of the display (Figure 20-24).
Note
If the navigation mode reverts to secondary
on deck during CV operations, the SAHRS
will default to a CV standalone align mode
(SAHRS continues to align as long as there
is weight on wheels); if a system reset is
initiated or occurs as a result of another failure,
the SAHRS will revert to a NORM
ground align mode. Attitude informationwill
not be available for approximately 45 seconds
when this occurs.
The secondary navigation mode can also be called
anytime the SAHRS is operating in its normal mode, by
depressingth e SAHR pushbutton.F or this condition, an
“M” will appear on the upper right of the display indicating
a manual selection has been made. Depressing
the INS pushtile at this time will again return the system
to the primary navigation mode with the “M” still ap.
pearing, indicating a manual selection has been made.
20.3.5.2.1 SAHRS Velocity Referencing. When
SAHRS alignment is complete it will generate its own
velocity outputs in a similar manner as the INS. Normally
this parameter should be satisfactory for backup
operation. In the event ofan inadequate SAHRS alignment
or degradation of SAHRS performance, it may
be desirable to select a velocity source for SAHRS
20-37 ORIGINAL
NAVAIR Of-F14AAD-1
N2lS7
Figure 20-23. INS In-Flight Align Formats
ORIGINAL 20-38
NAVAIR OWl4AAD-1
I
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WI97
Figure 20-24. Secondary Navigation Mode Manually Selected
refenzing. The sources available are shown on the
lower right-hand portion of the NAV SYSTEM AID
MFD format (Figure 20-25) and consist of the
following:
1. SYS - System velocity is the computed optimum
velocity using all valid velocity sources.
2. AIR - Air data computert rue airspeedw ith wind
compensation.
3. INS - INS-sensed velocity.
4. JTIDS - JTIDS-computed velocity.
When none of the above velocity sources is boxed,
the SAHRS will use its own velocity. This is the default
velocity mode.
20.353 Backup Navigation Modes The backup
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F-14D 飞行手册 Flight Manual 3(27)
