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SYSTEM DESCRIPTION, INSTALLATION, AND MAINTENANCE MANUAL
MCS--4200/7200 Multi--Channel SATCOM System
C. Failure Detection and Reporting Levels
(1) Failures are detected in the MCS system by a wide variety of tests. The immediate
result of failure detection is usually diagnosis of the failure to a specific component or
functional circuit group, on a specific SRU, in a specific LRU. However, some
detected failures may only be able to be diagnosed to a suspect SRU, or only to a
suspect LRU, or only to a pair or group of LRUs and the physical or logical
interface(s) between them. Three enumerated levels of failure diagnosis are defined
in Table 6-1.
Level
Level I
Diagnosis to the LRU level or its equivalent (e.g., a specific inactive bus, error, or
warning)
Level II
Diagnosis to the SRU (module or circuit card) level
Level III
Diagnosis to the component or functional circuit group level or equivalent (e.g., a
very specific error condition)
(2) All MCS LRUs implement Level I and, where possible, Level II failure detection. Level
I diagnosis primarily supports line maintenance. Front panel displays and automatic
reports to central fault/maintenance systems are only performed to Level I resolution
because they are primarily used to support line maintenance, which is typically limited
to LRU replacement. Level II and Level III diagnosis primarily support shop and
factory maintenance. Level II and Level III failure detection information is stored in
the LRU and system failure logs, and can be displayed on the commissioning and
maintenance terminal (CMT) pages.
D. LRU Coverage
(1) The LRU coverage is defined as the sum of all component failure rates covered by
the BITE circuitry within an LRU, divided by the total of the component failure rates
within that LRU. This coverage is greater than or equal to 0.95 as defined. The LRU
probability of false detection is defined as the sum of all component failure rates of
the BITE circuitry within an LRU divided by the total of the component failure rates
within that LRU. This coverage is greater than 0.01 as defined. The LRU coverage
includes the following:
• All SDU to avionic interfaces, where possible
• All MCS inter-LRU interfaces
• All power supply voltages
• All battery voltages
• All microprocessors/microcontrollers
• All memory devices (RAM, ROM, etc).
(2) All discrete drivers between the SDU and the avionics LRUs have over current
protection and open-circuit detection.
Honeywell International Inc. Do not copy without express permission of Honeywell.
Table 6-1. Levels of Failure
Description
23- -20- -35
Page 6--3
15 Jul 2006
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