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|  MIL-D-70789A (AR)
a DRU Coordinate Frame code, pointing device boresight angles,
and position offset distances. Vehicle boresight angles are
meaningless while the DRU is operating in Orientation 2.
Transitioning between Orientation 1 and Orientation 2 shall be
triggered by one of the following conditions: current
orientation attitudes crossing predetermined vehicle specific
limits; transition of the travel lock discrete signal; or receipt
of an IN TRAVEL LOCK or OUT OF TRAVEL LOCK command. The trigger
condition shall be specified using mutually exclusive Alternate
Orientation Configuration Definition flags (3.5.8.8m-r).
3.5.3.2.3 Anqular rates. The DRU shall provide three
pointing device rates: Pointing Device Azimuth Rate, Pointing
Device Pitch Rate, and Pointing Device Roll Rate.
3.5.3.3
Air transport mode. If stationary and in the Survey
Mode, upon receipt of an AIR TRANSPORT MODE REQUEST command the
DRU shall:
set STATUS S4/1 (DRU in Air Transport Mode); enter
the Exclusive ZUPT mode; and set STATUS S1/3 (DRU in Exclusive
ZUPT mode). Else, the DRU shall remain in the current mode and
set ALERT DATA D5/6 (Invalid Mode Request).
Prior to take-off, the DRU shall operate in the Exclusive ZUPT
mode and perform as in the Survey mode. The range of aircraft
motion prior to take-off includes: that induced by loading and
unloading equipment and personnel; engine starting and idling;
and taxiing.
Upon detection of take-off, as determined by either altitude
increasing significantly or high aircraft velocity (30 knots),
the DRU shall:
inhibit ZUPTs; inhibit ZUPT requests; fix
altitude; set STATUS S3/0 (Altitude Fixed) and S3/4 (ZUPTs
Inhibited). After take-off, the DRU shall set ALERT DATA D5/5
(Invalid Data Request) upon receipt of a RETURN SURVEY QUALITY
command.
Upon receipt of a TRANSPORT MODE COMPLETE command, signaling the
aircraft has landed, the DRU is stationary, and the transport
phase has been completed, the DRU shall: reset STATUS S4/1 (DRU
in Air Transport Mode) and S3/4 (ZUPTs Inhibited); set STATUS
S1/1 (Position Update Request); enable ZUPTs; enable ZUPT
requests; perform a ZUPT to control errors accumulated during
transport (this ZUPT is "forced" in that inertial velocities may
exceed the usual stop detection thresholds); release altitude;
and reset STATUS S3/0 (Altitude Fixed). If the DRU was operating
in the odometer mode prior to transport, the DRU also shall enter
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