...what caused such a decline in October
No FR TFS this winter, no LBA, and I think some of the sun routes eneded earlier than previous year. No increase on MAN/BHX since the loss of the jet capacity (-40/-28 on October 2011).
Perhaps they had pencilled in other route launches which didn't materialise for 2012 projection, AGP for instance. Still it shows adding new routes aren't always going to help the bottom line, building frequency on core services could have far more impact in growing numbers (and revenue).