For the first time, Airborne Warning and Control System (AWACS) are likely to be deployed here on the Republic Day for vigil from the skies during the parade where US President Barack Obama will be the Chief Guest.
The AWACS will monitor air space on and around Rajpath where the parade will be witnessed by Obama along with President Pranab Mukherjee, Prime Minister Narendra Modi and a host of other dignitaries.
Noting that it will be for the time that AWACS would be deployed for the Republic Day, official sources said the step is being taken in view of the heightened threat perception and apprehensions of aerial attack by terrorists.
The sources said the decision to deploy AWACS was taken at the request of the Americans who wanted India to tighten air space in Delhi when Obama is exposed during the Republic Day celebrations.
The AWAC detects incoming cruise missiles and aircraft from over 400-km away in all-weather conditions, and direction of air defence fighters besides picking up any low flying object which go undetected by normal radars.
AWACS, which has been integrated with Israeli technology on IL-76, will take off one hour before the function and keep circling around the national capital until the US President is out at the venue.
Changes are also being made in the flight path of civilian aircraft on that day in Delhi, with the minimum altitude being raised from 32,000 feet to 35,000 feet.
The Director General of Civil Aviation may issue a 'NOTAM' (Notice to Air Men) for diverting all flights overflying Delhi at the time of the parade.
Earlier, overflying plane above 32,000 feet did not fall in the category of no fly zone but now the height has been raised to 35,000 feet, the sources said.
However, no plane will be flying in the radius of 400 kms of the venue of Rajpath as against 300 kms on earlier occasions, they said.
This means airports adjoining Delhi like Jaipur, Agra and as far as Lucknow or Amritsar may not operate flights when the function will be on in the national capital.
Sticking to the past practice, no plane will land or take off at the Indira Gandhi International Airport during the time when Republic Day will be on at Rajpath.
American officials may also part of all radar stations and control rooms that have been set up for the visit of the US President.
Union Home Minister Rajnath Singh said earlier in the day that "all security arrangements are in place. There will be no problem anywhere."