On 7 January, two aircraft lost separation while flying above Nawabshah, Pakistan. A Pakistan International Airlines (PIA) Boeing 777-200 (AP-BGY) operated domestic flight PK301 between Islamabad and Karachi and an Emirates Airline Boeing 777-300ER (A6-EPS) operated flight EK516 between Dubai, U.A.E. and Delhi, India.
Both aircraft received a TCAS resolution advisory, the Emirates Boeing 777 was instructed to descend while the PIA Boeing 777 got the instructions to reduce its rate of descent.
The civil aviation authority of Pakistan reported a near collision occurred and suspended three air traffic controllers involved into the occurrence. An investigation has been opened.
A word of explanation: the traffic collision avoidance system (abbreviated as TCAS, and pronounced tee-kas) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control (ATC), and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC).
The next step beyond identifying potential collisions is automatically negotiating a mutual avoidance manoeuvre (currently, manoeuvres are restricted to changes in altitude and modification of climb/sink rates) between the two (or more) conflicting aircraft. These avoidance manoeuvres are communicated to the flight crew by a cockpit display and by synthesised voice instructions.
The airborne collision avoidance system is mandated by the International Civil Aviation Organization (ICAO) to be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5,700 kg or authorised to carry more than 19 passengers.