the reading incident
The Air France aircraft was heading north, while the British Midland was heading south. Despite being second in the sequence, the Air France pilot was ordered by Air Traffic Control to turn in towards Heathrow's final approach before the British Midland. This meant that this plane was turning directly across the path of the British Midland. The controller gave this order on the basis that immediately afterwards he would order the British Midland pilot to turn in front of the Air France jet.
But what if the controller could not immediately get through to the British Midland pilot? The BBC's whistle-blower says that happens on a relatively common basis. Sometimes he says the radio system is used to 90 percent of its capacity, a claim rejected by NATS Swanwick general manager. In lay terms, it's the equivalent of getting through at the first attempt when making a mobile phone call at a crowded event like a football match. Whilst you hope this happens, sometimes it takes two or more tries.
The recently retired controller said: "The radio sometimes becomes blocked, pilots are slow to take the turn, the air traffic controller may have got distracted by something else. Had that turn not taken place then extrapolation of the radar picture demonstrates that the aeroplane from the north would have passed very close indeed -- probably less than a quarter of a mile -- straight across the front of the one from the south. That is extraordinarily close. That is a shocking incident".
In terms of timings, he estimates from the radar that collision could have been as little as 20 seconds away: "Whether they actually would have hit -- very, very difficult to judge but they got extremely close and way past the point, way, way past the point, at which the regulator should be getting involved with this type of operational culture."