Air India Flying Returns offers an upgrade against miles on Air India flights, both domestic and international. The upgrade can be requested up to two hours prior to the flight, but has some horrible rates for mileage upgrades. Earlier, there was a fixed chart, which was 75% of the miles of an economy redemption to go from Economy to Business class, but now, can be between 60% to 190% of the redemption miles of the sector (60% for Y and B RBDs, and 190% for the cheapest RBDs such as E and S)
While this is not the best value on Air India miles in the current set up, since you could anyways redeem a J class ticket for 200% of Economy class miles, sometimes this may be the only option. To get an upgrade, you can walk into the Air India city offices, or the airport reservation counters at the airport (which AI calls Curb side instead of Kerb side). You can also make a call to the Air India call centre. They will have a look at your ticket to determine the Booking class of your ticket, and after that check if there is upgrade space available on the flight (same as award inventory).
They need to reissue your ticket after deducting miles from your account. If they cancel the flight after, you get all your miles back, but if you cancel your flight, they will deduct 500 miles to process a refund. Also, you earn miles on your original class of booking.
Of course, you can also now redeem your Air India Miles for upgrades on other Star Alliance carriers as well.
While it is bad value, still it may make sense to sometimes redeem miles for an upgrade rather than buy a ticket for business class.
Have you ever redeemed miles for an upgrade on Air India flights?