Module 7 2014 Q8

[James Bishop]

My attempt at 2014 Question 8. I'm relatively familiar with RAMS subjects but electronic systems aren't my forte so some of the answers to the last part of the question may be a bit off the mark.

[PJW]

My attempt at 2014 Question 8. I'm relatively familiar with RAMS subjects but electronic systems aren't my forte so some of the answers to the last part of the question may be a bit off the mark.

This was one of the questions (or rather one based very closely on this one but we slightly altered) that was chosen to be discussed earlier in the year at the mod1/7 day; I was expecting that someone from there may have written up and submitted their answer but it is good to get an independent view.
The presentation I produced for discussing the similar question there should still be available from Dropbox:
https://www.dropbox.com/s/tc312hk7xma30j....pptx?dl=0

 
First impressions count and the first thing that strikes about the answer is how neat and clearly set out it is.  Whereas there are no marks for this per se, the examiners struggle with interpreting poor writing very frequently and can’t give any credit for what they can’t decipher.  In contrast your paper would come as a welcome relief and before they read a word would already be in the mood to be favourably disposed.  If you can write neat lock capitals fast enough, then do so!
 
First part-
Comprehensively covered- possibly a little long for available marks- perhaps items iv) could have been incorporated within i).  The diagram at the end was a good idea, but in an exam you could have got the idea across quicker by only drawing the first half.
 
Second part-
Simple and sweet. Marks seem generous for that.  I think I'd have added some assumptions to qualify the answer.
MTTR- the figure could be that quoted by the manufacturer to repair item in ideal circumstances, but the figure one really wants to know is that which is experienced in reality.  Hence in the real world one might need to add to that number
a) the time taken before the technicians are alerted to the failure,
b) the time taken to get to site (and quite possibly arrange a suitable time with the signaler to get access),
c) the time taken to diagnose the fault,
d) if need a new part, possibly a trip to the stores to collect,
e) the re-test / re-calibration time
Of course in the real world, the technicians may have other things to attend to, so may not be able to respond immediately when advised, or perhaps when working on a fault may be called off elsewhere to something considered more urgent.
You would not write all this in the exam, but well worth pointing out that the MTTR quoted by the manufacturer and the MTTR as seen by the signaler before the equipment is signed back into use may be very considerably larger. 
Similarly another thing we are not told is whether there is any need for scheduled routine maintenance; if there is then this also detracts from availability so it isn't only the quoted MTBF that constitutes the downtime.
As the examiners regularly say "State Assumptions" and the mark allocation here certainly suggests they were wanting more and this is what I'd have given.  Querying something instead of taking everything at face value is I believe a means by which one demonstrates experience.

 
Third part-
iii)   As far as railway signalling is concerned, most of the assets are relatively fixed rather than vehicles or similar.  Far more emphasis for first line maintainers to get to the equipment- if it is of some form of modular construction they may of course simply identify the defective Line Replaceable Unit and interchange it for a spare.  As far as the equipment is concerned (after any re-testing etc.) it is now considered operational, although of course the part of it item that provoked the failure is still faulty and then this would either be at its life’s end or would itself be recovered to repair facility as you suggested.  For some items of equipment, such as point machines, exchanging for a spare is really far from easy and generally it is better to replace components on site, even if that means dismantling in less than ideal conditions.  Obviously when considering wiring within a building, then really no option at all.  Therefore your wording slightly incorrect for typical railway signalling context, but would be applicable to ETCS on board or items such as that.  Generically good item, but could have been worded better.
Note that whereas the parts above and below say "electronic system" this portion just says "system", and hence I would take this as a broad hint that this section was to be interpreted more widely.

iv) Should have given a little more detail and in particular recognise that clearing the fault is one thing, but being ready to re-enter into operational service is something extra.  If there is a defective length of 48core cable requiring a replacement section to be jointed in, there is a lot still to do after the cable is intact before the technician can sign the signalling back into use!  The cable jointers may have been off-site for a shift or so before the “downtime” as seen by the operations department trying to signal a train service has ended!  Another area where your relative inexperience within the railway signalling domain is leading you to give an excellent generic answer which isn’t 100% aligned to the context of the IRSE.

v) In conjunction with this item, it is worth adding that one of the factors that relates to the “competence of the maintainer” is for frequently they have to do the task.  Hence if a certain type of equipment is very unreliable and they are always having to fix it, then they will become very familiar and often have a good idea of exactly what is wrong before they even get to it.  Conversely if there is a highly reliable bit of kit that just works for years on end then suddenly malfunctions, the maintainer may have no idea where the manual for it is kept, what tools they might need and may not have ready access to spare parts.  So it is not just down to the person and their generic abilities- to a certain extent the “field maintainability” as measured by total downtime of an item can actually be adversely affected by it having excellent inherent reliability and vice versa
 
fourth part-
iii)  even better if the system itself can tell the human what needs to be done one step at a time.  Photocopiers are very good at telling untrained users how to clear paper jams for example.
vii). Not just about the design of the product itself as an entity; both the design of the product and the site application design which incorporates within a signalling system must consider issues such as access space around it without having to contort themselves to work within it, whether the person then blocks their own light, if there is a touch potential issue between some items on a TN and others on an IT power supply and similar.  As a young graduate, I once deliberately connected the black lead of an oscilloscope lead to the black (negative) bus bar of the power supply of an item of Telecomms equipment in order to fault find- what I didn’t know, but very quickly established in no uncertain way, is that Telecomms batteries are always positive earthed- they can supply a lot more  Amps than a scope lead screen can carry!
There is a reason why scope leads are earthed; there is a reason why's the always was the positive of the Telecomms battery that is earthed, but the combination isn’t great and hence a hazardous condition exists.  Add in a naïve person undertaking what in the circumstances and unsafe act and ==> INCIDENT.  So maintainability does need to consider the system in its environment, not just as a stand alone item in splendid isolation.
 
A comprehensive list, suitable for the available marks.  Didn't think any "off the mark" but perhaps some would have more relevance to other systems.  However I do think that ideally the list would have included some reference to:

• the maintainability of software (language, structure, documentation thus enabling any necessary modifications in years to come)
  
• the ability to undertake diagnosis remotely and perhaps even update the software remotely without having to physically access- particularly important for a distributed system.  Just think about how Microsoft and Apple for example undertake operating system upgrades.
  

Generally it is always good when producing a list of items to ensure that it is as diverse as possible and thus covers the entire range, so whereas you had included ten distinct items, it would have been even better to show the widest interpretation of maintainability.  Most electronic systems nowadays have some element of firmware within and hence it seems reasonable to include these bullets on the list in preference to the some of those that you had listed which, whereas applicable, would be more so for a mechanical system.


Overall I thought this was an excellent answer, only marred by not demonstrating as much domain understanding as the examiners would be expecting- sure it would still get a Credit though!