Two passenger planes in 'serious' near-miss after aircraft accidentally climbs to the same level as another

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Two passenger planes were involved in a ‘serious’ near-miss after one of them did the opposite of the air traffic controller’s instructions - and flew up instead of down.

The near-miss occurred over Bulgaria as the two planes flew to Istanbul.

One, an Atlasjet, was instructed by air traffic controllers to descend but the pilots allegedly initiated a climb instead. The error resulted in the plane flying parallel to a Turkish Airlines aircraft just 1.4miles away.

Two passenger planes were involved in a ‘serious’ near-miss after one of them did the opposite of the air traffic controller’s instructions - and flew up instead of down. The near-miss occurred over Bulgaria as the two planes flew to Istanbul

An Atlasjet operated aircraft was instructed by air traffic controllers to descend but the pilots allegedly initiated a climb instead (file photo)

The incident, which took place on September 8 this year, only came to light on Thursday.

According to the Aviation Herald, the Atlastjet operated flight KK-6112 was flying from Zurich to Istanbul at the time.

While at a position of about 140 nautical miles (161miles) south east of Sofia and 130 nautical miles (150 miles) of Istanbul, controllers at the Sofia centre instructed Atlasjet pilots to descend from an altitude of 35,000ft to 31,000ft.

At the same time, Turkish Airlines TK1966 was travelling from London Gatwick to Istanbul.

While at the same coordinates as the Atlasjet plane, the Turkish Airlines aircraft was instructed to descend from 37,000ft to 33,000ft.

However, instead of descending as instructed, the Atlastjet aircraft started to climb according to the report.

At the same time, Turkish Airlines TK1966 was travelling from London Gatwick to Istanbul and was flying to the same coordinates (file photo)

Both planes ended up flying at 36,300ft with a horizontal separation of just over a mile.

Controllers in Sofia were able to issue instructions to both aircraft in time to prevent a collision - the Atlasjet plane flew left while the Turkish Airlines jet flew right.

The planes continued to descend to their correct altitudes after that and were able to safely land in Istanbul, according to the Aviation Herald.

In Bulgaria, aircraft are normally required to have a vertical separation of at least 1,000ft, according to the Bulgarian International Virtual Aviation Organization, but in this case, the planes were flying at zero vertical separation.

The incident, considered serious, is currently being investigated by Bulgaria's Air Accident Investigation Unit (AAIU).

MailOnline Travel has contacted Atlasjet, Turkish Airline and Bulgarian AAIU for comment.