The UK Air Accidents Investigation Branch has issued five safety recommendations in its final report on the near mid-air collision of a German-registered Cessna Citation CJ1 business jet and a Turkish Airlines Boeing 777 on 27 July 2009.

The AAIB says the CJ1 - registration D-ITAN - climbed too quickly after taking off from London City airport. The light jet was less than 0.5nm from the 777 - registration TC-JJA - when the CJ1 crew took evasive action. Investigators found that the 10-year-old CJ1's traffic alert and collision avoidance system (TCAS) was not functioning at the time of the incident.

The CJ1 carrying two crew and one passenger had been cleared to depart London City with an initial climb to 3,000ft (915m). The pilot read back the cleared altitude as 4,000ft, an error that was not noticed by the tower controller, says the AAIB. At about the same time, TC-JJA was cleared to descend to an altitude of 4,000ft on its approach to London Heathrow.

"D-ITAN climbed through 3,000ft while turning right and passed TC-JJA on a nearly reciprocal heading approximately 0.5nm away and 100-200ft below," says the report.

TC-JJA generated three TCAS resolution advisories in short succession, but the aircraft did not follow the commands. D-ITAN was unable to generate resolution advisories.

"The crew of D-ITAN saw TC-JJA in time to take effective avoiding action. Had the aircraft been in instrument meteorological condition, this would not have been the case and TCAS would have been the only barrier to a potential mid-air collision," says the AAIB. It has issued five safety recommendations:

That the UK National Air Traffic Services demonstrates that appropriate mitigation has been put in place to reduce significantly the risk of an accident resulting from a level bust by an aircraft departing London City airport or on the base leg turn positioning to land at Heathrow airport.

That London City amends all standard instrument departures so that they terminate at an altitude of 3,000ft.

That London City removes step climb procedures from its standard instrument departures.

That the UK Civil Aviation Authority considers whether the carriage of TCAS II should be mandated for aircraft operating in those parts of the London terminal manoeuvring area where London City standard instrument departures interact with traffic positioning to land at Heathrow.

That the Turkish civil aviation authority ensures Turkish Airlines TCAS training complies with the International Civil Aviation Organisation airborne collision avoidance system training guidelines.

Source: Flight International