Safety was “much reduced” when a passenger jet came too close to another plane near Stansted Airport, a report said.
An Airbus A320 had to pull out of attempting to land as a smaller Saab 340 was preparing for take off on 12 February 2019, an Airprox Board report said.
Air traffic controller actions did not resolve the conflict, while the Stansted Aerodrome Traffic Monitor (ATM) was ineffective, the report said.
It added there had been a “breakdown” in crew resource management in the A320 which had distracted them and meant they did not comply with an order to turn left in a “timely manner”.
An airprox was recorded when the A320 was at an altitude of 3,000ft and the Saab was at 2,400ft.
The craft came within 87m (285ft) of each other horizontally – nearer than the minimum recommended of 4.8km (3 miles) horizontally and 305m (1,000ft) vertically.
The Airbus had gone around once before successfully landing.
One possible cause for distraction in the Airbus was that the commander was training and his performance being monitored, the report said.