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ating safety and reliability of the overall system, and was enacted as an IEC
international standard (IEC 62278) in 2002.
What should be carried out in 14 stages from the conceptual to the de-
commissioning and disposal are defined in RAMS, as shown in Fig.2.
Fig. 2. The “V” representation
By implementing the requirements of RAMS at each stage of development
and managing risks in consideration of both the frequency of hazardous occur-
rences and their severity, it becomes possible for the system to be maintained
effectively and economically.
When new system is to be set up on site (tenth cycle of RAMS), test data
of a variety of systems, sometimes a report of safety property verification by
a third person and risk analysis at a time of design by supplier are verified.
The risk analysis data which we receive before setting up on site is the
'designed value'. The risk evaluation mechanism when we operating is neces-
sary as a system user and we think that risk analysis of RAMS can be applied
for operating systems as a method of evaluating reliability [4] [5].
3.2
Problems in failure verification related to railway signalling
system in JR East
Meetings that deal with break down are held once a month with each supplier,
in which the cause of failure is specified and measures taken with all related
equipment when equipment breaks down. That is to say, in our present sys-
tem of maintenance, we tend to repeat the RAMS stages 11 (Operation and
maintenance) to 13 (Modification and retrofit), according to need. When a
problem occurs, we often merely go back to the 13th stage and make a repair
(see Fig.1, Cycle A).
But when looking at the overall railway signalling system, we need to
evaluate the appropriate reliability level of equipment over the entire system
