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25 years after Charkhi Dadri: How flying became safer

The air collision resulted in two major changes to aviation rules globally

spicejet takeoff rep pti Representational image | PTI

Charkhi Dadri changed the way we fly. Or, to be precise, Charkhi Dadri changed the way pilots fly planes.

The major changes were two. One, they got ACAS. Two, English became the language of the skies.

This correspondent remembers seeing the shocking news on the ticker about an air collision late on the evening of November 12, 1996, and rushing to the office of H.S. Khola, then director-general of civil aviation. My colleague, Rajesh Ramachandran, had already left for the spot with photographer P. Mustafa; my senior (now dear departed) D. Vijayamohan had rushed to the airline offices in the airport. My job was to cover the DGCA and the civil aviation ministry.

That night itself Khola, still in shock and sweating despite the winter cold, told us whatever details he had learnt by then. The next evening, when we met him again, he told some of us, informally of course, that he would move heaven and earth to make ACAS mandatory on airplanes. He did. That was the first major aviation reform after Charkhi Dadri.

ACAS is short for aircraft collision avoidance system, a kind of radar that is installed in aircraft by which a pilot comes to know whether another aircraft is on his flight path. Actually, it is the computer on one aircraft speaking to the computer on the other one, and alerting pilots if both are on the same flight path. Khola got the full support of civil aviation minister C.M. Ibrahim in the Deve Gowda government. Within weeks of the Charkhi Dadri collision, India notified the International Civil Aviation Organisation (ICAO) that no commercial plane that can carry 30 or more passengers would be allowed to land on an Indian runway if it has not installed ACAS. Now we have even ACAS-II, an advanced version.

Till ACAS came in, it had been the job of the air traffic controller to keep planes as away from one another as possible, both vertically and horizontally. Two planes can be allowed to fly at the same height if they are away from each other wing to wing. That is called horizontal separation. Two planes can also be allowed on the same flight path if they are at different heights. That is called vertical separation. It was—and is—the job of the air traffic controllers (ATCs) to ensure that planes are separated horizontally and vertically from one another.

However, ATCs faced problems because they had to confine all planes to a very limited airspace. The skies may be metaphorically open, but in reality they are not. Most of the airspace is actually closed. The Indian Air Force controls most of the airspace and allows civil planes to fly only through designated routes and paths. This is essentially to ensure that rogue planes don't fly in. In fact, only a year earlier before the accident had a Latvian airplane quietly sneaked into the Indian airspace and dropped small arms in Purulia district of West Bengal, for some rebel outfit. Since then, the IAF had been on enhanced vigil, and refusing to open up more airspace for civil flights.

There were also other problems. Even planes flying over India between European and Southeast Asian cities and not touching down in India too had to confine themselves to the designated routes and heights for the Indian radars to monitor them. Thus the Indian civil airspace was crowded during the night—virtually bumper-to-bumper traffic—when more flights operated.

Anyway, following Charkhi Dadri, the Indian Air Force expanded the civil airspace. Secondary surveillance radars were soon installed in airports, enabling ATCs to read the altitudes of flights without being told by the pilots.

One major reason why the collision happened was because the Saudi Air plane was taking off through the same 'driveway' as the Kazakh plane was using for landing. The Delhi Airport quickly developed its runways after the crash so as to allow separate 'driveways' for take-off and landing.

The other big revolution was making English the language of the skies. Investigation into the Charkhi Dadri collision revealed that the commander of the Kazakh Air flight could not follow the instructions given to him in English. He descended from the assigned height of 15,000 feet to 14,500 and further to 14,000 and even further because he misunderstood the instructions from the ATC.

Soon after the disaster, India proposed to ICAO that certain minimum English skills should be made mandatory for pilots flying international sectors. It took nearly 10 years to convince the ICAO, where much resistance was put up by non-English-speaking countries, to issue directions that all aircraft personnel—pilots, flight engineers, flight navigators, air traffic controllers and aeronautical station operators—need to have their English language proficiency evaluated to Level 4 of ICAO standards. They would be tested every three years.

Level 4 skills, incidentally, is an ability to understand and express "mostly accurate on common, concrete and work-related topics" and a "vocabulary range and accuracy [that is] ... sufficient to communicate effectively”. The person should be able to "often paraphrase successfully when lacking vocabulary in unusual or unexpected circumstances”.

Charkhi Dadri, thus, remains as a tearful turning point in the evolution of human flying.

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