Two passenger jets came within 700 feet (213 metres) of each other after a mistake by a British air traffic controller, according to a near-miss report.
The error was made by a controller “during a period of high workload”, the UK Airprox Board (UKAB) said.
He gave an instruction to increase altitude to a Boeing 737 leaving Stansted Airport, Essex, which was meant for another aircraft from the same airline, the UKAB said.
This caused the former to climb “into confliction” with a Boeing 777 approaching the airport, according to the report.
The official minimum separation between the two jets should have been 1,000 feet (305 metres).