R --------------------------------------------------------------------------
R LOC and G/S deviation data computed by the primary and monitor
R DSPs are checked by the system processor against stored values
R for accuracy. If an error is detected, the SSM of the
R appropriate deviation word is set to NCD or FW, depending on
R the type of error until another test sequence shows that the
R deviation data have passed the test. If no error is detected,
R the deviation words SSMs follow the sequence given in the
R table above.
R 2_ Receiver face test
R The receiver face test request is treated as the MCDU request
R except that the on-ground condition is not taken into account.
R The sequence is identical to the functional test sequence,
R with the receiver face LEDs being additionally controlled to
R reflect the status of the unit.
R 1EFF : 051-060, 1 34-36-00Page 29 1 1 Config-1 May 01/05 1 1 1CES 1
R 3 Power-on test_
R The power-on test request is initiated each time the ILS is
R powered "off" for longer than the 200 ms play through time and
R back on again. The power-on test is treated just as the
R functional test described in para. 1_ above, except that the
R SSMs of the LOC and G/S remain set to No Computed Data (NCD)
R for the entire 16-second test sequence. If a fault condition
R is detected during power-on test, the SSM of the LOC and/or
R G/S are set to FW until the detected condition is cleared.
R Additionally, during this power-on functional test, the
R ability of the DSPs and I/O to identify faulty ARINC output
R data and shutdown the bus, is tested, and the RAM and ROM
R tests are performed.
R **ON A/C 001-004,
R (4) ILS monitoring
The ILS monitoring is based on the on-line monitoring performed
during normal unit operation, and on test modes which provide a check
of all deviation-affecting circuitry.
(a) On-line monitoring
1 Redundant computations paths_
The monitor processor provides a secondary processing path
that is dissimilar and independent of the primary path. Every
1ms the monitor processor processes the same sample set of
digitized IF data as the main processor DSP (main DSP) but
performs an independent validation and deviation computations.
Deviation computation implementations in the monitor processor
and the main DSP are dissimilar because of:
- different programming languages used to code the algorithms
in the monitor processor and the main DSP,
- different canonical forms of the digital filters used in the
implementation of the two algorithms.
2 Deviation validation_
The computed deviations are checked for validity through
reasonableness tests performed on the modulating tones.
These tests are performed independently on the LOC and G/S
signals. The SSM of the respective output word is set to No
Computed Data (NCD) based on both the monitor and the main DSP
validity determination, within 500 ms, under the following
conditions:
R 1EFF : 001-004, 051-060, 1 34-36-00Page 30 1 1 Config-1 May 01/05 1 1 1CES 1
3
_
-
the Localizer signal depth of modulation of the sum of the 90 Hz and 150 Hz tones is less than 70 per cent of its nominal value,
-
the Glide Slope signal depth of modulation of the sum of the 90 Hz and 150 Hz tones is less than 70 per cent of its nominal value, the glide slope deviation is flagged,
-if either of the two RF signals is not detected on the selected channel while there is no internal failure,
-either the 90 Hz component or the 150 Hz component of the modulating signal is absent from the detected output and the modulation depth of the remaining compound retains its nominal value.
Deviations cross-comparison The computed deviations in each path are cross-checked independently with the deviations from the alternate path every 50 ms. The DP receives the deviations computed by the monitor DSP through a dual-port RAM and compares them to the most recent deviation outputs transmitted on the ARINC 429 bus. A comparison failure is deemed to have occurred if both deviations disagree by more than:
-
plus or minus 0.0065 DDM for Localizer deviations in the range of -0.310 to +0.310 DDM. plus or minus 0.0325 DDM for Localizer deviations less than -0.310 DDM or greater than +0.310 DDM.
-
plus or minus 0.009 DDM for Glide Slope deviations in the range of -0.350 to +0.350 DDM. plus or minus 0.045 DDM for Localizer deviations less than -0.350 DDM or greater than +0.350 DDM.
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