The airspace towards North of Delhi was a no-fly zone for commercial airlines on 27th February 2019.This was due to India-Pakistan tensions which forced airlines to suspend flights to and from airports.
A no-fly zone is a territory over which aircraft are not permitted to fly. Its objectives include:(a) Security of a particular area (b) Security of a particular structure (c)Security of particular group of people.Mostly,such zones are set up in a military context, somewhat like a demilitarized zone in the sky.
Civilian No fly zone are communicated in NOTAM(NOtice To AirMen). A NOTAM for No fly zone will include map coordinates and altitudes for the borders, as well as a short explanation.No fly zones are often put in place for events such as the 2017 G20 Hamburg summit.
In India, the various No fly zones are (a)The Taj Mahal (b)The Rashtrapati Bhavan (c)Parliament Building (d)Prime Minister’s residence, and other important centers in New Delhi (e)The airspace around many Defence and Indian Air Force bases (f)The Tower of Silence, Mumbai (g)Mathura Refinery (h)Padmanabhaswamy Temple,Kerala (I) Bhabha Atomic Research Centre (j)Sriharikota Space Station in Andhra Pradesh (k) A 10-km radius no-fly zone over Kalpakkam nuclear installation, Tamil Nadu and (l) All Refineries.