KARACHI, June 17: Preliminary investigations into Tuesday’s near-miss involving PIA and Airblue aircraft has established that the incident took place because of a mistake of the air traffic controller who failed to issue the warning to the pilots.

Sources said the pilot of PIA Boeing 747, which was flying from Karachi to Islamabad, continued to ascend as it was cleared to climb to its designated altitude of 37,000 feet by the air traffic controller though the Airblue’s Karachi-bound Airbus A320 appeared in the same air corridor.

While the Airblue flight AB-207 was flying at its assigned flight level of 36,000 feet, its pilot observed the PIA plane coming from the opposite direction some 65 miles short of Nawabshah, said sources.

“The Airblue pilot immediately initiated the climb after receiving Traffic Collision Avoidance System warning

and took the aircraft up to an altitude of 37,500 feet,” they said.

“The PIA aeroplane with 51 passengers and 15 crew members and the Airblue one carrying 153 people including seven crew members had to sharply manoeuvre over Nawabshah, after emergency warning alarms sounded.”

The sources said the vertical separation between the two aircraft was recorded to be 400 feet whereas standard mid-air separation between two aircraft is 1000 feet. “When the computer of aircraft detects the vertical separation minima less than standard, it gives a radar advisory to the pilot who initiates descend or ascend profile to bring the aircraft to the standard level.”

The sources said the Civil Aviation Authority had launched the investigation into the incident and tapes and video recordings of radar had been preserved. However, the investigation has not yet been completed.

Aircraft of the two airlines suffered a similar near-miss in December last year in the same area.

Preliminary investigation into the December incident had reportedly established that either faulty equipment or pilot’s error had led to the sudden turbulence, which left a passenger and a crew member slightly injured.