In message , at 01:07:31 on Thu, 19
Aug 2010, Stephen Furley remarked:

If there was no alternative to isolating the brake on the failed train
we don't know why another train, or locomotive, with a functioning
brake wasn't coupled behind it.

This seems to be the easiest to answer ... where would you find a
locomotive from, and how long would it take to get to the site with (as
appears to be the case) service trains in the way. The other possibility
would be to take the nearest train out of service, and use that -
although the decision was apparently made to pull using a train from the
north rather than push with one from the south.
--
Roland Perry