IndiGo-KLM planes' air scare: Preliminary probe hints at ATC lapses

New Delhi: A preliminary inquiry into an air scare involving an IndiGo and a KLM aircraft last year has pointed out several lapses on the part of the Air Traffic Control, including delayed response and use of wrong call sign to communicate with one of the airlines.

The IndiGo plane from Delhi to Bengaluru and the KLM airline from Amsterdam to Kuala Lumpur narrowly averted the mid-air collision on November 2, 2016.

The probe found five errors on the part of the Air Traffic Control (ATC).

As the lateral and vertical distance between IndiGo's IGO 977 and KLM 811 flights reduced beyond permissible limits, an automated warning or Predicted Conflict Warning (PCW) went off.

However, as per the probe, the ATC ignored this for 82 seconds.

At this point, "the required standard lateral and vertical separation which should be 10nm and 1000 feet was reduced to 3.6nm and 200 feet, respectively," said the report.

Further, as the ATC tried to communicate with the IndiGo plane to reduce its height, it used a wrong call sign at least five times, it said.

"The controller instructed IGO 977 to descend to FL340 but inadvertently used call sign as Vistara 977. Controller used wrong call sign five times. Subsequently, the controller instructed KLM to ascend to FL360," said the report.

In the meantime, the IndiGo aircraft continued to climb, thereby, further reducing the distance between itself and the KLM plane. This continued until the pilot realised that the ATC instructions were meant for it and not Vistara, it said.