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SYSTEM DESCRIPTION, INSTALLATION, AND MAINTENANCE MANUAL
MCS--4200/7200 Multi--Channel SATCOM System
(b) A stuck switch on the CMT or LRU front panel does not cause PAST to remain
active. Any switch activity is ignored while PAST (or POST) is executing.
(c) The HPA and HSU inhibit PAST while the aircraft is airborne, except when PAST
is initiated through the CMT, which is permitted at any time. The HPA and HSU
cannot properly function if not receiving valid command words from the SDU
containing the air/ground status and command information. Under these
conditions, the HPA and HSU are not usable by the SDU. PAST is only permitted
while the aircraft is on the ground, or when the airborne/on-ground status is
unknown. In lieu of the airborne/on-ground status information from the SDU, the
HPA and HSU permit PAST as though the aircraft is on the ground.
(d) A system-wide PAST is initiated in the SDU when commanded by:
• Entry through the SATCOM control and display unit (SCDU)
• Entry through the central maintenance computer (CMC)
• Entry through the central fault display system (CFDS)
• Command from the CMT
• Activating the PTT switch (SDU TEST) on the front panel.
(e) A stuck switch on the SDU front panel does not cause PAST to remain active.
Any switch activity is ignored while PAST (or POST) is executing.
(4) Continuous Monitoring
(a) Continuous monitoring (CM) of the BITE circuitry does not interfere with the
normal operation of the system. Instead any failure condition is recorded and
reported. Continuous monitoring operates as a background task at all times,
even during functional testing. Functional test failure codes that are identical to
the continuous monitoring codes (except for the MSB of the level 3 code)
indicate cases where the functional test differs in some way from the companion
CM test. Those CM failures detected during functional testing (e.g., maintenance
and status word failures) are logged as CM failures, not functional failures.
F.
Failure Recording
(1) The SDU records CFDS internal failures at all times. The SDU only records CFDS
external failures while receiving a valid All Call DC1 Command if a Douglas or Airbus
CFDS is installed. Internal failures are defined as those internal to the SATCOM
subsystem. External failures are defined as those external to the SATCOM
subsystem. If a Boeing CMC (or no CFDS) is installed or if valid DC commands are
not available, then the air/ground status is used to generate pseudo DC states of
DC0 (aircraft on-ground) and DC1 (aircraft airborne).
(2) The HPA records internal failures at all times. The HPA only records external failures
while the aircraft is airborne, based on the status of the weight-on-wheels discrete
(on-ground vs. airborne). Internal failures are defined as those that have the same
Level I code as the LRU recording the failure (i.e., 01 for the SDU, 04 for the HGA
HPA, and 07 for the LGA HPA). External failures are defined as those failures not
having the same level 1 code as the LRU recording the failure.
Honeywell International Inc. Do not copy without express permission of Honeywell.
23- -20- -35
Page 6--7
15 Jul 2006
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