The UK Airprox Board says that there needs to be a greater awareness among pilots and controllers of the risks inherent in mixing high-performance aircraft with slow traffic at general aviation airports.

Reporting on a near collision beween a business jet and a light piston-powered aircraft in the circuit at Biggin Hill aerodrome near London, the board noted that this risk will increase as the number of very light jets in operation grows, because their performance equals or exceeds that of existing business jets.

The category B airprox event ("the safety of the aircraft was compromised") took place on 17 January 2010 at Biggin Hill in good weather under visual flight rules, when a Cessna Citation Sovereign that was climbing after take-off from Runway 21 had to manoeuvre to avoid hitting a Cessna 172 Skyhawk that had been cleared to join the right-hand visual circuit from the dead side.

Avoidance was assured only because the tower controller, seeing the conflict developing fast, transmitted: "Have you seen the 172?" The Citation pilot looked up from engaging the autopilot, and replied: "Negative, oh! affirm! Whoaa!" and rapidly levelled out.

The inquiry found that the both pilots were complying with correct procedures and had been cleared for their respective manoeuvres. The conflict had arisen because the Citation crew, when cleared to do so, had lined up and taken off particularly quickly, rotating less than half-way down the runway and climbing at a high rate.

The controller had anticipated that, by the time take-off took place, the 172 that was about to cross the runway end at circuit height to join the downwind leg would be well clear. In the event it was not well clear, and the Citation passed 100ft (30m) below and less than 200m behind the 172 having been alerted to its presence at the last moment.

The board's verdict is that the event could have been avoided if the tower controller, before giving take-off clearance to the Citation, had ensured that the crew had visual contact with the 172.

Source: Flight International