Two aircraft have come perilously close to a mid-air collision over London in what could have been a “serious incident”.
According to a report from the Air Accidents Investigation Branch (AAIB), a passenger jet operated by Turkish Airlines came within half a mile of an impact with a private business jet in July 2009.
The incident occurred over London City Airport.
Pictured: The trajectory of the two jets over London in June 2009
With both aircraft at approximately 4,000 feet above the capital, the Citation 525 jet was about 100ft to 200ft below and half a mile away from the Boeing 777 passenger plane, heading to Heathrow with 232 people on board.
AAIB investigators found the control tower at London City had cleared the German-owned business jet to climb to 3,000ft. However, when the flight crew acknowledged the instruction, they said they would be climbing to 4,000ft.
This incorrect instruction from the plane – known as a “readback” mistake in the aviation industry - was not noticed by the controller at the tower.
Simultaneously the Turkish Airlines jet was descending to 4,000ft on approach to London Heathrow Airport.
Had the aircraft come closer the “only barrier to a potential mid-air collision would have been traffic collision avoidance systems (TCAS)”, the AAIB added.
However, the report found the Turkish flight crew had failed to follow three commands issued by on-board collision-avoidance systems.
The Citation jet did not have equipment known as TCAS II.
In response the AAIB recommended the TCAS II equipment should be made mandatory for planes flying in the London area.