Its not possible, because if we detach slip coaches at salem it needs minimum of 20 minutes, but the actual ernakulam express halts in salem for only below 5 minutes. So, for detaching coaches takes time, and it affects actual train timing. But at erode, train halts for 20 minutes, amd thats the right time to detach the coaches. That's the reason to run slip coaches from erode to Rameswaram