13-04-2016, 03:03 PM
Dorothy,
A thorough answer to a seemingly easy, but quite difficult, question. Seems a little long for 30 minutes but your exam technique may be to do so. There probably is a pass in there but the question hasn't been fully answered even though there are some important and relevant points in there.
First point is a suggestion; answer each question fully rather than split. Technique tends to mean the subject is repeated anyhow so context won't be lost. Not sure there are eight marks of consequences.
Good for picking up TPWS is not for stopping trains at red aspects. However, later on you discuss about overspeed mitigation and this should be mentioned at the same time. So, by definition, TPWS is not for SPAD mitigation. It is to remind an operator that an speed or movement authority is/is-to-be exceeded. Because of this and arguably, TPWS not energising is not a WSF per se, I agree, this was a bad example to use. TPWS would only activate the on-board equipment if a failure (operator error, signal reversion etc.) has/is taken/taking place. I would be interested to see other's views on this.
WSF2 - the failure described is generic. The WSF failure is a miscount out (so out==in when physically out!=in) so the section believes it is clear when it is occupied, i.e. more permissive. A miscount where the section shows occupied is a RSF. The early part of the answer discussed RSF whereas it shouldn't but improves further on. The "This is particularly..." paragraph isn't correct for a WSF question.
Suggestion for a WSF would be a relay sticking, incorrect indications etc. A more permissive indication to the train/operator than should be provided is the acid test.
A thorough answer to a seemingly easy, but quite difficult, question. Seems a little long for 30 minutes but your exam technique may be to do so. There probably is a pass in there but the question hasn't been fully answered even though there are some important and relevant points in there.
First point is a suggestion; answer each question fully rather than split. Technique tends to mean the subject is repeated anyhow so context won't be lost. Not sure there are eight marks of consequences.
Good for picking up TPWS is not for stopping trains at red aspects. However, later on you discuss about overspeed mitigation and this should be mentioned at the same time. So, by definition, TPWS is not for SPAD mitigation. It is to remind an operator that an speed or movement authority is/is-to-be exceeded. Because of this and arguably, TPWS not energising is not a WSF per se, I agree, this was a bad example to use. TPWS would only activate the on-board equipment if a failure (operator error, signal reversion etc.) has/is taken/taking place. I would be interested to see other's views on this.
WSF2 - the failure described is generic. The WSF failure is a miscount out (so out==in when physically out!=in) so the section believes it is clear when it is occupied, i.e. more permissive. A miscount where the section shows occupied is a RSF. The early part of the answer discussed RSF whereas it shouldn't but improves further on. The "This is particularly..." paragraph isn't correct for a WSF question.
Suggestion for a WSF would be a relay sticking, incorrect indications etc. A more permissive indication to the train/operator than should be provided is the acid test.
Le coureur