PETALING JAYA: Indian authorities have ruled out the possibility of missing Flight MH370 flying undetected over their airspace.

According to a report by the Times of India, air traffic controllers at Kolkata said the aircraft could not have avoided the radars at Kolkata Flight Information Region.

They were responding to a statement by Prime Minister Datuk Seri Najib Tun Razak of the possibility that the missing plane might have traveled over Indian airspace right up to the Kazakhtan-Turkmenistan border.

Indian air traffic controllers guild secretary Sugata Pramanik said that while flight MH370 could have avoided detection on the secondary surveillance radar, the blip sent out by the huge Boeing 777-200ER would surely be spotted by the Indian Air Force (IAF) that uses primary surveillance radars to detect intrusions.

"If an aircraft wants to avoid being seen, they can easily become invisible to civilian radar by switching off the transponder.

"But it cannot avoid defence systems. The IAF has radars in multiple installations across the country and it is inconceivable that none of them spotted the odd blip with no flight clearance," he was quoted as saying.

There are nine air defence identification zones in the country that are manned 24 hours to prevent an enemy aircraft from violating Indian airspace.

According to guild member Sushil Mondal, all hell would break loose if the IAF detected an aircraft that did not have air defence clearance.

Any plane flying through Indian airspace is first required to submit the flight plan and manifest to the air traffic controls in its flight path. This is then relayed to the air force for permission.

"There are times when the Air Force finds a blip that does not match a flight plan.

"That usually happens when flight plans go missing at their end due to a system or link failure.

"They then immediately contact us for information. If the plane's flight plan isn't of suspicious nature, a clearance is granted.

"Or else, it is asked to return to wherever it came from.

"In case, we too don't have any information of the aircraft, there will be trouble and the Air Force scramble jets to take the plane down. Nothing of the kind happened last Saturday," said Mondal.

Recently, the IAF scrambled a Sukhoi Su-30MKI fighter jet in the western sector after noticing an unidentified 'blip' crossing over from Pakistan, It turned out to be a weather balloon.

Kolkata airport has an automatic dependence surveillance radar and controller-pilot datalink communication that enables it to not only trail planes when it is in the radar zone of 60 nautical miles or nearly 120 km and beyond through very high frequency radio but also through the data link when the plane goes out of voice communication range.

There are large areas in the Kolkata Flight Information Region, particularly over Bay of Bengal, that have no radar coverage at present.

A radar has been installed in Andaman and Nicobar Islands, but is yet to be commissioned.