In the early hours of Sunday, July 24, 2022, two Pakistan International Airlines jets avoided a mid-air collision thanks to their onboard collision avoidance technology. The incident happened around 160 nautical miles (296 kilometers) northeast of Dubai, in Iranian-controlled airspace. On Monday, Iran's Civil Aviation Authority (CAO) issued its Final Report on the incident.

Two routine flights in different directions

The two Pakistan International Airlines (PIA) aircraft involved were a Boeing B777-200, registration AP-BGJ and an Airbus A320-200, registration AP-BLW. The B777 was operating PIA flight PK-211 from Dubai International Airport (DXB) to Pakistan's Islamabad International Airport (ISB). The A320 had departed from Qatar's Doha Hamad International Airport (DOH) en route to Peshawar Bacha Khan International Airport (PEW). Immediately before the incident, the B777 was at flight level 360, and the A320 was at FL350.

Initial reports said that the B777 (PK-211) was cleared to descend to FL200, directly into the trajectory of the A320 (PK-286). Both aircraft received TCAS (traffic collision avoidance system) Resolution Advisories, with ADSB data showing PK-211 climbing to FL363 and PK-286 descending to FL346. The official report from Iran's CAO has a different view, concluding the probable cause as:

"Based on radar service within control area (CTA), the controller's instructions and clearances for both traffics were correct, and the cause of the TCAS/RA serious incident was the pilot's misunderstanding, leading to mistakenly (PIA211) commence descent without receiving any clearance from Tehran ACC controller."

The Iran Aircraft Accident Investigation Board (AAIB) investigated the incident, with their report published in English on the CAO's website. To ensure accuracy, the following is quoted directly from the CAO report, without any grammatical changes.

At 004122 UTC PIA211 B772 was traveling on airway A453 to BND then airway M324 to MOBET at FL360 when the pilot requested the controller to advise any level restriction at MOBET position, and the controller told him, "PIA211 expect FL200, 20 NM before PATAT, report when ready for descent." The granted message was acknowledged by the pilot accordingly. At 004254 UTC, another flight, PIA286 A320 at FL350 on reciprocal track airway via airway Z151 to KHM and then airway A453 to ZDN was identified by Tehran radar controller, and following the pilot's request, this flight was instructed to proceed directly to NABOX waypoint.

Here is what happened

At 005107 UTC, the controller instructed the PIA211 to proceed directly to PATAT waypoint and expect FL200, 20 NM before PATAT and stand by for descent. The pilot of PA211 acknowledged the message correctly. At 005307 UTC, the pilot of PIA286 declared TCAS/RA descending. Immediately the controller told the PIA211, "You were told to stand by for descent." At 005407, another flight on frequency told the PA211 without expressing his callsign: "you were never given a clearance; you were told to call when ready." The CAO report adds: "On July 27, 2022, some parts of the above information were disclosed to the social media by the airline."

PIA Boeing 777-200ER
Based on the Iran CAO report, the PIA B777 descended without correct clearance from ATC. Photo: Getty Images

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In its analysis, the CAO said the controller had modified the "flight route to some extent" and later on, "when the longitudinal separation between the two aircraft declined by 10 NM, while there was 1,000 ft vertical separation, PA211 commenced descent to FL200 without receiving any prior descent clearance." Both aircraft obeyed the TCAS advisories, and when the two were cleared from each other, the B777 descended to FL200 and was handed over to UAE radar for further descent.

In a final sting in the tail, the CAO said that "the pilot of PIA211 did not report TCAS/RA to Tehran ACC." In the findings, it also expressed its displeasure with PIA, saying: "Disclosure of the incident report details to [the] public by Pakistan International Airlines spokesperson before issuing the Final Report was against international regulations as per Annex 13 and related documents."

Presumably, radar data and audio tapes support the final report's findings, so is this as clear-cut as it sounds?

Source: Aviation Herald