Tamworth-bound Virgin Airlines plane in near miss with United Airlines flight near Sydney Airport

The near miss occurred about 2.25pm on January 22 after the United Airlines (UA) flight from Sydney to San Francisco took off from Sydney Airport, just after the Virgin flight - codenamed VOZ1153 - bound for Tamworth.

The planes came within 60m vertically and 1,843m - or about 1 nautical mile - laterally, about 2km from Sydney Airport.

The near miss did not cause injury to anyone involved but triggered an automatic investigation by the safety regulator, the Australian Transport and Safety Bureau (ATSB).

READ ALSO:

The ATSB said the "lost of separation" was classified as a "serious incident".

The investigation found air traffic control noticed the aircraft near one another.

"The Sydney departures controller observed UA870 turning right and towards VOZ1153 and quickly issued unambiguous and immediate instructions to both aircraft to rectify the situation and re-establish the required separation," the report revealed.

Investigators said the UA flight was meant to turn left after reaching 1500 ft but climbed straight ahead to 2100ft, and then turned right.

"Air traffic control detected the loss of separation and issued interventional instructions to both aircraft," the ATSB said in its investigation report, made public this week.

"The required separation was re-established and both flights continued without further incident."

ATSB investigators said the UA pilot "incorrectly amended the flight management computer" that had been cleared for departure, and the amended plan was "not effectively communicated".

"The pilot flying probably did not effectively communicate the changes made to the FMC to the crew. The FMC departure specific coding was also not effectively cross-checked by the pilot monitoring or relief pilots prior to take-off," the report said.