NSG
the 52 SAG exists almost entirely for this purpose and is co-deployed with aviation assets so they can be anywhere in India within a 3-4 hour flight, if the situation requires a more immediate response then local units will have to create a plan. As it stands CISF QRT only exists to create an outer cordon and await NSG as far as airside ops go, they are more focused on CQB on the terminal side.
52 SAG has their main force at Delhi's IGI airport so my assumption is that IGI is designated the preferred airport to send any hijacked aircraft to and then NSG will be on scene almost immediately but if you're a hijacker you'd be incredibly foolish to chose to land at a capital city.
There are a few state QRT/ERT units that have trained for something like this, I guess as a contingency for when NSG cannot arrive in time.
That said CISF QRT needs to be re-thought, they should be trained and equipped to a level where they can board a plane and take out a hijacker in an emergency situation. As it stands they are basically just given a BPJ and declared a 'commando'. There is a QRT at every major airport in India and they will be the first responders to any such crisis and should be equipped accordingly, NSG cannot be everywhere at all times.
I'm actually laughing, not one individual in any of the units in the list above will have the required training or equipment to conduct an airplane intervention (force one are probably the only ones to have done some dry runs but their capacity is too limited to even seriously consider it).
52 SAG's entire organisation is orientated around aviation
For something as relatively simple as getting onboard a plane that 20-30ft in the air only NSG has the means.
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Some units outside of NSG may have done some dry runs once for boarding an airliner but it's something 52 SAG does on a regular basis all over India from all Indian airlines. NSG is the only unit in India that is legally able to request any airline registered in India to give them an aircraft for transport or training purposes and obviously they are the only unit in India that has their own aircraft training simulator:
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^ the MARS (and Sherpa based aircraft intervention vehicle) were inducted specifically because their assault ladders can reach up to the height of an A380's upper deck
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