The radar blip that led to a mid-air scare as the special aircraft carrying Prime Minister Manmohan Singh [Images] prepared to land at Delhi airport on Tuesday night, was caused by an Indian Air Force Dornier aircraft, which was flying "behind and above" the VIP flight path, official sources said on Wednesday.

The Dornier plane was in "no way on the flight path of the PM's aircraft," sources in the Airports Authority of India said quoting preliminitary investigations into the incident.

The blip on the radar was detected by the Air Traffic Control.

The IAF Boeing 737 with the prime minister on board landed safely though 16 minutes behind schedule, but not before the IGI Airport was put on high alert and security officials went into a tizzy.

A team of officials from Director General of Civil Aviation, AAI, Bureau of Civil Aiviation Security and other agencies is investigating the incident, the sources said.

The officials are also looking into any possible malfunction in the radar in detecting certain parameters of the Dornier's flight path, they said.

As the PM's plane, which was coming from Jamshedpur, was in its landing approach over Delhi airspace, the ATC suddenly noticed an unidentified object on the radar.

An emergency drill on the ground was quickly put in place while air controllers asked the pilot of the aircraft to hover over the Delhi airspace for 16 minutes before clearing the plane for landing, the sources said.

The pilot switched off the aircraft's Instrument Landing System and guided the plane on a changed flight path manually while making the final approach, they said.