An air traffic controller with a high risk of fatigue was on duty when a Virgin Australia jet cut in front of a Qantas plane at Sydney Airport in August, safety investigators have revealed.
The Australian Transport Safety Bureau (ATSB) has released two preliminary reports into close-call incidents at the airport in August.
The reports did not make findings or recommendations, but outlined the sequence of events, and the conditions at the time.
The two reports are among six investigations underway into close call incidents at the airport.
The first incident happened on August 17, when Virgin flight VA1589 was taxiing to the domestic terminal after diverting from Newcastle because of bad weather.
About 9:40am, the air traffic controller told the Virgin crew to "follow the Qantas to vacate ahead, hold short runway 25".
The first incident involving Virgin flight VA1589 took place on August 17. (Supplied: ATSB)
According to the report, the Virgin captain read back only the hold-short instruction, and the controller did not recognise the incomplete read back and moved on to other tasks.
Shortly afterwards, the crew of Qantas flight QF420 saw the Virgin jet approaching a taxiway intersection at a speed that suggested it would not give way.
They were forced to stop the aircraft using normal braking.
The Virgin jet passed in front of the Qantas aircraft, and its crew did not realise there was a conflict until the Qantas crew queried it with the controller.
The controller was removed from duty for the rest of the day, and later told investigators their view of the taxiway intersection from the tower was limited by equipment in the tower cab.
The taxiing incident involving Qantas flight QF420 and Virgin flight VA1589. (Supplied: ATSB)
Fatigue concerns
The air traffic controller, according to the report, was rostered to finish at 8:50pm the night before the August 17 incident, and start again at 5:30am the next day.
They were the only controller in the tower, with a high predicted fatigue level.
The report said predicted fatigue did not mean a controller was necessarily fatigued, only that they were at risk based on their roster.
The controller described their mental fatigue level at the time as "fine and alert", and that they were "fit for duty".
The report also noted that Airservices Australia, which provides air traffic control at Sydney, does not have a fatigue management system approved by the Civil Aviation Safety Authority.
In a statement, Airservices Australia said it acknowledged the interim reports and would "review the findings once these investigations are complete".
Pushback conflict
The second incident happened on August 25, when a controller cleared a Jetstar A320 operating as JST745, to push back from bay 59 onto a taxiway.
About 30 seconds later, the same controller cleared a QantasLink Dash 8, with the call sign QLK427D, to taxi along the same taxiway, past the A320's bay.
The Dash 8 crew saw the A320's tail moving backwards and stopped about 100 metres from the bay.
The A320's pushback driver and dispatcher also stopped the pushback and warned the flight crew.
Flights QLK427D and JST745 at their closest point. (Supplied: ATSB)
The Jetstar jet was then towed back onto its bay so the Dash 8 could pass behind it.
Three air traffic controllers told the ATSB that push backs from some gates were prone to conflicts, because aircraft push straight onto an active taxiway rather than an "apron".
The tower shift manager and a supervising instructor also said the area could be a "black spot" where aircraft were not always detected.
The shift manager was returning to Sydney after time at another airport, and was working under supervision while their endorsements were reinstated.
Three trainees were also on shift.
The controller on duty said they "felt fine", but had "not had many days off in the past month".
Aircraft taxiing routes. (Supplied: ATSB)
ATSB says crews acted in incidents
ATSB chief commissioner Angus Mitchell said both incidents were mitigated because flight crews and ground staff identified the conflicts and acted accordingly.
"As such, an important safety defence acted appropriately, but our role is to establish why crew actions were necessary to prevent a more serious outcome,"
he said.
Mr Mitchell said investigators were yet to determine whether staffing contributed to any of the six incidents they are examining or whether it was an underlying condition being effectively managed by Airservices.