As the ALCos, WDM-3A, WDG-3A, were aging, Railway board decided to discontinue their service in mainline and use them for shunting duties. So the ERNAKULAM diesel shed decided to scrap ALCos but they retained some ALCos for the small sections where still it is diesel traction. Usually the power will be WDP-4D but sometimes WDM-3A or WDG-3A will be also coming as power from ERNAKULAM Jn to Kollam Jn. Once such instance happened and I was able to spot and capture an ERNAKULAM WDG-3A with Ernakulam Jn - Velankanni Express. This WDG-3A will power the train till Kollam Jn and from there PONMALAI WDP-4D took charge of the train after reversal. So after ages I got to see an ALCo in the mainline.