Except during a major war, nations have never been more nervous about the behaviour of aircraft over their territory than they are now

Since 11 September the USA has made it no secret that an aircraft departing from the route agreed with air traffic control (ATC) for no apparent reason is liable to fighter interception. Clearance for shoot-down can now be arranged with remarkable rapidity because Department of Defense representatives with a hotline to the Pentagon and the White House now stalk the major ATC centres.

If pilots think this is science fiction in the sense that the shoot-down would never really happen even if interception occurred, they should think again. If non-US pilots think they are safe, especially over their own territory, they should realise that all the major Western nations have made preparations in case the perpetrators of the New York and Washington DC terror attacks should swing their sights onto another symbolic target. So the recent discovery that most airline pilots have forgotten the visual procedures for interception that they once learned when qualifying as pilots has to be taken seriously. What is more, the International Air Transport Association has found that major agencies like the International Civil Aviation Organisation and the US Federal Aviation Administration publish differing procedures.

In an interception, if communication with ATC is live and the airliner's transponder continues to provide ATC with the aircraft's identification, all should be well. Also, direct contact with the interceptor should be attempted using the emergency frequency 121.5mHz or the military's more often used UHF band 243mHz. And if a loss of communication is the result of an identical maintenance error in an aircraft's radio "boxes" and not the result of a major aircraft systems failure, at least the aircraft is likely to be able to adhere to its flight planned path and its transponder might be working. So what is the problem?

However unlikely it is for a modern air transport aircraft to lose all its communications options, it has happened before and it will happen again. But if there is a sudden silence for whatever reason, and the aircraft's destination is New York or Washington DC, survival depends on White House nerves as the aircraft approaches the cities.

The USA is not the only potential target. Transfer the scenario to an aircraft cleared, on entry to the London terminal information area, to expect a westbound approach to London Heathrow: Downing Street is not going to wait until the aircraft is at 3,000ft (920m) over the City before mandating a shoot-down because the result would be the kind of disaster that the military action is aimed at preventing.

Looking back, air-to-air shoot-downs of commercial transport were usually the result of inadvertent penetration of sensitive airspace. Korean Air discovered this twice (1978 and 1983) on entering Soviet airspace. There was no radio failure there, but communications failure there certainly was. The Korean aircraft (respectively a Boeing 707 and a 747) were not in touch with Soviet ATC because they did not realise that they were in Soviet airspace. In addition, Korean only had VHF and HF radios, while the Russian fighters only had UHF. Even if they had found a common frequency they would not have had a common language - Soviet military pilots had no reason to learn international ATC English.

Just because 11 September has made the skies a more highly charged environment, it does not mean that the same basic rules about uncleared penetration of foreign airspace do not still apply. If an aircraft makes a navigation error, or if airspace is in dispute, shoot-down can legitimately occur. But there are other reasons for knowing what the rules on interception are. If an aircraft suddenly experiences a major systems failure and the nearest diversion is hostile territory, a knowledge of what an intercepting pilot is trying to communicate may be the difference between a safe landing and shoot-down. In April this year an aggressive interception of a US Navy reconnaissance aircraft caused collision damage which forced it to divert to land on Hainan Island, sovereign Chinese territory.

So the causes for interception are many, as are the combinations of circumstances in which communications between the three parties - ATC, intercepted and interceptor - can fail. There has never been a time when an interception should be taken more seriously and resolved more quickly by whatever form of communication is needed at the time, because the potential is there for a completely needless shoot-down and the loss of an aircraft full of innocent people.

Source: Flight International