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|  MIL-N-81604C(AS)
Para 3.4.1.2 (cont)
establish whether or not they are functioning properly. These
tests along with the monitoring circuits, the malfunction flags,
and the special tests performed only in the BIT mode shall pro-
vide a 90 percent probability of isolating a failure to the WRA
level. In addition, built-in test equipment shall be provided
which tests equipment voltages and those portions of the equip-
ment which are used in the backup modes selected when the ANCU
is inoperative.
3.4.1.3 Aircraft Power Failure - Navigation performance shall
not be degraded by voltage transients or total power drop out of
duration up to, but not exceeding, 10 seconds in flight and five
seconds on the ground, except for functions which depend upon
26 VAC supplied by the aircraft (i.e., synchro and converter
excitation) . A battery will be used for this purpose, and it
*
The equipment shall be
shall be part of the Power Supply Unit.
designed to accommodate power interrupts which, in cumulative
total, equal 10 seconds of time in any two hours of equipment
*
operation. Refer to 3.5.3.4.
3.4.2 Equipment Accuracy
3.4.2.1 Inertial Navigation Set Accuracy - The INS shall operate
for up to six hours mission time, within the performance limits
specified in table V, for the alignment times and conditions
specified in 3.3.11. Refer to 3.4.1.1.3a(1) and 3.4.1.1.3a(2).
The specified align periods assume the availability of continu-
ous power during the initial warm-up phase and the availability,
during carrier alignment, of alignment reference data as speci-
fied by AR-57. This performance may be achieved by means of
thermal modeling of inertial set errors, rapid warm-up of the
inertial set, or any combination of methods that provides the
required performance. For alignment and navigation accuracies
in modes other than unaided free inertial, refer to appropriate
AR documents; (e.g., AR-65 for E-2C).
3.4.2.2 Attitude Reference Mode Accuracy - In this backup mode,
the components within the IMU shall contribute a level reference
error of no greater than 7 minutes (one sigma). The additional
level error due to aircraft dynamics and earth rate may be cal-
culated from the curve shown in figure 4. The components within
*
the IMU shall contribute an uncompensated heading drift error of
no greater than 0.5 degrees/hour (one sigma). The sine latitude/
magnetic slaved heading error input, when provided by the CAU as
as described in 3.4.1.1.3c(1) and (2), has a scale factor
29
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