Confusion over call signs assigned to the US-hired military cargo aircraft led to the grounding of the plane at the Mumbai international airport on Friday night.
The Ukrainian-made AN-124 aircraft, owned by Russian private airline Volga-Dnepr, claimed that they had taken a clearance from the Director General of Civil Aviation to overfly the Indian air space with a call sign attributed to civilian aircraft.
However, the officials of the IAF's ATC claimed they had heard a different call sign generally attributed to a defence aircraft before it was set to enter the Indian air space, officials said.
The confusion over the call signs made the authorities to ask the aircraft to land at the Mumbai airport after which a thorough check of the plane was conducted.
During the checking, the authorities found only two vehicles meant for American officials fighting against the Taliban in Afghanistan and boxes full of medicines, they said.
An IAF spokesperson Wing Commander T K Singha told PTI here said the aircraft was allowed to get airborne after the External Affairs Ministry gave the Air Operations Routing (AOR) authority to fly over Indian airspace changing the call sign of the plane to that of a defence aircraft.
IAF sources said the AN-124 had been operating on the same flight plan in the last fortnight and had come under adverse notice because of its call sign.
"The aircraft used a civilian aircraft call sign VDA 4466, whereas its original call sign was REACH 813, which implied it was a military cargo aircraft," they said.
Since obtaining a military clearance for using Indian air space by foreign military aircraft is cumbersome, it has to go through MEA, Intelligence agencies and then IAF. The operator adopted a short cut by obtaining a civilian call sign for the aircraft, they added.
"The aircraft, chartered by the US military, took off from Diego Garcia, a US military base on an island near Mauritius in the Indian Ocean," the officials said.
The aircraft used for long-range delivery and air-dropping of troops and heavy military cargo had intruded into Indian airspace around 2000 hours last evening.
No IAF fighter jet had scrambled to escort the intruding aircraft, as it clearly followed ATC radio calls and landed in Mumbai at 2240 hours, the IAF spokesperson said. IAF officials said there were a total of 18 persons on board the aircraft, including a five-member crew.