Remember the 80’s when, if you picked up the heavy receiver of your enormous telephone, sometimes you could hear your neighbour talking to her aunt? Perhaps the BlackBerry-carrying Generation Y would not have heard of cross-connection but in the congested Delhi airspace, it is still a reality and a dangerous problem.
Air traffic controllers at the Indira Gandhi International Airport complain about regular disturbance and sometimes cross-connection on the wireless VHF (Very High Frequency) over which they talk to and instruct pilots. Not only they have to keep repeating instructions because of the disturbance, sometimes cross-connections lead to scary situations when one pilot start following instructions meant for someone else.
With dreaded fog season fast approaching and the number of flights from IGIA being increased this winter, the Delhi ATC said communication disturbance would pose a big problem.
“The system has become like the old radio sets on which you could hear a crackling sound while changing stations. The VHF is our basic tool and only communication medium with the pilots,” said a senior ATC. “It is even more important than the radar.”
Another ATC said that it takes a lot of time just for the pilot to establish his/her identity. “What should be done in one transmission takes four-five, leading to more stress,” he said. “There is too much interference as the range width is poor. We have five different frequencies distributed between the tower, area, approach and other controls,” he said.
When ATCs instructs a pilot, he/she has to read it back and the instruction is considered as acknowledged. “Until they read it back completely, we have to keep making transmissions,” he said.
Incidents of cross-connections are more worrying. “Sometimes when we give instructions to one pilot, it is picked up by a pilot on a different frequency,” he said. “A few months back, a pilot started descending though the ATC had instructed another plane to do so. Thankfully, we detected the movement on radar and the plane was put back on right altitude after frantic transmissions,” he said.
“Different bandwidths are allotted to ATC but if two bands are too close and there is wrong tuning, such overlapping happens,” said a senior official of the Directorate General of Civil Aviation (DGCA).
Thanks to disturbance on the bandwidth, the aircraft radio sometimes also picks up FM music channels instead of instructions. “The communication equipment needs upgradation and also need world-class technicians,” he said.
“The clarity on VHF depends on the weather condition. During cloudy weather there are crackling sounds on the frequency,” said Director General of Civil Aviation Kanu Gohain. He, however, said that he has not received a written complaint about the problem.
Senior ATCs said many complaints have been made to the Airports Authority of India, which is responsible for running the Air Traffic Services. An AAI spokesman, however, claimed that the communication system is advanced and upgraded regularly.