January 28, 2009 4:32:54 am
A mid-air disaster was narrowly averted a day after the Republic Day when more than seven aircraft lost their contact with the air traffic control (ATC) at the Netaji Subhas Chandra Bose International Airport for more than half-an-hour after an unknown transmitter blocked their VHF (very high frequency) communication.
The mysterious incident occurred around 9:45 am when a Jet flight from Bangkok to Kolkata left the Yangon ATC and approached Kolkata. It first contacted the east area control frequency,which then lost all contact with the seven other approaching aircraft.
Realising the problem,the east control immediately informed the pilot to connect to west area control around 9:55 am. Accordingly,the pilot contacted the west area control,which too immediately lost contact with all other aircraft.
As the aircraft was fast approaching Kolkata,it was then asked to contact the approach frequency. A similar problem was encountered there as well,but the flight was finally given a green light for safe landing by approach at 10:18 am.
Meanwhile,the east and west control had instructed the other seven domestic flights to hover for more than 20 minutes. During this time,none of the other flights could establish any contact with the approach frequency.
None of the other frequencies could be contacted except for area control south,while the Jet flight landed. After it landed,everything was normal, said an ATC official.
The ATC works with many frequencies at a time like area,tower,approach and HF (higher frequency). Today,each time we established contact with the Jet flight,we lost contact with the other flights, said another ATC official.
There was not much risk as we could see the flights in the main and secondary radars. Thus,at all points,we were aware of their position and height, said P K Singhal,the executive director at the airport. He added that besides this,there are other standby frequencies that can be used in case of emergencies.
An investigation has been ordered to see if it was technical failure or some lapse on the part of the ATC. Some unknown transmitter on a similar frequency was blocking the VHF. We are looking into it but we have not been able to identify the transmitter, Singhal added. There are some star procedures that pilots are supposed to follow in case of communication failure, said a ground and flight safety official. There are about 5-6 frequencies that can be used in case of emergencies. Usually,we get through one frequency or the other. If not,we follow the standard procedures and stay put at whichever position we were given the last clearance, said Capt M K Singh,an Air-India pilot. Besides,the VOR instrument in the aircraft tells us the direction and distance to the approaching airport, he added.
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