On an average, around 7 or 8 locos per month (sometimes more / sometimes less) are sent to BSL ELS Workshop as 'dead' loco with Pune-BSL Exp. Please see the following post which I had already posted here on 29-Jan-2016!
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Discussions with staff revealed following information: The locos (WAGx) which are due for scheduled maintenance (like IA/IB/IC Schedules or POH or AOH) or locos requiring repair / re-cabling or some such work, are sent as dead loco to BSL Electric Loco Shed using Pune-BSL Exp. When such loco comes to Pune, TLC...
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(Train Loco Controller) can not take the risk of using this loco as main / driving loco. Failure en-route will lead to delays / traffic congestion or in worst case can even cause some kind of accident, etc. If such thing happens, higher authorities will ask why that loco was used to haul the train (Exp or Goods). So, instead of taking all these risks, sending the loco as a dead loco is safest option. The works which BSL ELS does can be seen at the URL click here
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Please see the few blog entries /blog/post/1743622 and /blog/post/1739066 and /blog/post/1734836 and /blog/post/1731124 and /blog/post/1724368 and /blog/post/1715749 for all such locos being sent to BSL in the past!