KARACHI, Dec 23: Preliminary investigations into Wednesday's mid-air incident involving PIA's flight PK-309 indicate that either faulty equipment or pilot's error led to a sudden turbulence which left a passenger and a crew member slightly injured.
Sources close to the inquiry said the Karachi-bound PK-309 climbed and descended within a minute at around 8:14pm while crossing an Islamabad-bound aircraft (PK-370), though the mid-air vertical separation between the two aircraft did not warrant such a move on the part of the pilot.
"The aircraft was never on a collision course with another one, either PK-370 or ED-406 of Air Blue, as it had sufficient separation with them," they said. The sources said the PK-309 had already crossed the Lahore-bound flight ED-406 of Air Blue at 8:11pm before it climbed and descended.
PIA spokeswoman Samina Pervaiz said it would be premature to comment on the matter because the inquiry by the Civil Aviation Authority was still in progress. "Let's wait for the outcome of the inquiry and set aside all presumptions," she said.
However, some sources in the national flag carrier said the incident had taken place due to the faulty altimeter of the aircraft (PK-309), which might have incorrectly read the plane's height.
They said the ED-406 and the PK-370 were assigned the flight level of 37,000 feet, which they maintained throughout their journeys. "However, PK-309 could not maintain its assigned flight level of 36,000 feet due to erratic altimeter readings as it flew on different levels at different times throughout its cruise," the sources said.
Aviation sources said the PK-309 could maintain the assigned flight level till 8:12pm and it climbed to 36,200 feet and then 36,300 within the next minute while crossing the PK-307 which was flying at 37,000 feet.
"The standard mid-air separation between two aircraft is 1000 feet. When the computer of PK-309 detected the vertical separation minima at 700 feet, it gave radar advisory to the pilot who initiated descend profile so as to bring the aircraft to the standard level," the sources said.
They said the same aircraft (PK-309) later operated from Karachi to Kuwait on a greater vertical separation (2,000 feet) as desired by the airline due to the faulty altimeter.
In his report, pilot of PK-309 stated: "Good flight visibility on IFR. Aircraft seen coming from opposite direction showing 800 feet above, followed by traffic radar alert asking for 1,500 feet per minute descend. Evasive action taken, the other aircraft responded RA climb after crossing altitude difference of 700 feet."
The pilot of ED-406 said in his report: "While flying from Karachi to Lahore and maintaining the assigned FL370, close to position 'Murli' at approximately 8:10pm we picked up PK-309 coming from opposite direction at FL360.
Due to good visibility at the level we had visual contact with him, observed him on the TCAS (Tactical Collision Avoiding System) as well with 1000 difference. While he was getting closer we saw the difference reduced to 900 feet and while he was approximately below us the difference reduced to 800 feet.
We got TA (Traffic Alert) followed by RA (Radar Advisory) asking for climb only at the time of visual crossing immediately followed by 'clear of conflict'. The TCAS warning was reported to Karachi Radar by the opposite aircraft PK-309.
I confirmed my FL370 with Karachi Radar which was reported to show flight level 370 to Karachi. The crossing was accomplished with a normal crossing separation of 100 feet. There was no TCAS warning on either aircraft.
Aircraft equipment, auto-pilot operation and Radar Control confirmed that ED-406 maintained flight FL370 throughout its cruise segment. No deviation from the assigned level of 370 for cruise was made at any time. No near miss incident took place and ED-406 operated normally."
The 179 passengers on the PK-309 included federal Information Minister Shaikh Rashid Ahmed, Senator Waseem Sajjad, Supreme Court Judge Deedar Hussain Shah and MNA Kunwar Khalid Younus of the Muttahida Quami Movement.
