Though No.117 managed a fairly long freight consist as a test train the passenger coaches are heavier and she needs help with the Cuarto Mail between Bodjio and Cumbre. This help is provided by a light engine move in advance of the train as far as Bodjio. When the train arrives it pulls clear of the junction, allowing the helper to be attached on the rear.
The reason for doing it this way is because of an awkward reverse curve as trains leave Grande and the risk of derailments this incurs.
The addition of a helper loco for the climb from Bodjio to Cumbre adds operational interest to the railway thus making it much more fun playing trains on the layout, and that’s what the hobby is all about.