SkyScanner Salem to Kochi Flight at Rs.998

Such fares are common on Alliance air since they mostly serve airports and routes that are not serviced by other airlines. I've flown with them a couple of times and the flights were empty.   

If you're asking how they manage to stay afloat, it's because they're still owned by the govt. They got over 1000 crores in this budget after being given a similar amount last year in addition to 600 cr debt relief.   

So, by making use of this deal you're just partly vasooling your tax rupees.