Most of the world's air traffic control, on the ground and in the air, is conducted procedurally, but at some airports that is not good enough

Inadvertent runway incursion - on the priorities list for preventative action by the US Federal Aviation Administration and Europe's Joint Aviation Authorities - has produced another tragedy. Under the circumstances prevailing at Milan Linate airport on 8 October, where controllers had already adopted low visibility procedures (LVP), there is nothing more they could have done to prevent this accident, except to close the airport because of poor visibility. If that statement highlights the shortcomings of the system, it is intended to. But to understand where the industry should go now, it is necessary to examine the basis for the well-tried existing systems.

In this case, as in many others, a pilot had made a mistake, but had either not realised it or had not declared it. And because the controllers had no independent way of monitoring the CitationJet pilot's actions, they had to act on the assumption that he was doing what he had been cleared to do. He confirmed that he was, but in that very act unknowingly passed wrong information.

No matter whether in the air or on the ground, that situation defines the weakness of procedural air traffic control (ATC) as opposed to the positive kind of ATC which controllers use if they can see the aircraft they are controlling, either directly from the tower's visual control room (VCR) or on radar.

In the procedural situation, one fundamental safety component has been lost: the ability of one part of a team to check the actions of the other. The reality is, however, that there is more procedurally controlled airspace in the world than radar-controlled, and far more airports without surface movement control radar than with it. Linate is just one of them.

The fact is that an active system of monitoring is intrinsically safer than a passive one. Deciding that all airports should stop operating in LVP conditions unless they have someform of surface movement radar, however, would regularly close most of the world's provincial airports - and some of the major international ones.

Only a tiny proportion of the world's airports have surface monitoring radar, and even among those the level of sophistication varies massively. Effective versions of this potentially lifesaving equipment have only been on the market for the last 20 years, and major airports have only begun installing them in any numbers in the last 10 - the FAA has now made it compulsory for all the USA's major airports.

The primary cause of this accident is that a pilot took the wrong taxiway, and the controller had no way of knowing. The pilot had even been offered a "follow-me" vehicle but rejected it. Perhaps the controller, who clearly had reasons for offering the "follow-me", should have insisted on it, but Linate is a small downtown airport and the pilot only had a choice of two taxiways from the apron he was parked on: one to the north and one to the south.

It indicates the power of assumption in human errors. A cursory check of his airport charts would have made it clear to the pilot where he had been told to go, so it looks likely that he had already decided by which route he would be cleared. Finally, the clarity of the taxiway markings in poor visibility will be a matter for the investigation. Those simple considerations almost exhaust the issues confronting the pilots and controllers on the day.

So are there any new lessons to be learned from the Linate disaster - lessons that could not have been learned from Taipei airport when the Singapore Airlines Boeing 747-400 in October last year slammed into heavy equipment on a closed runway, or from the world's worst ever air crash at Tenerife in 1977 where two 747s slammed into each other? Poor visibility was common to them all, as was the tendency of the airports to bad visibility, and none of them had surface radar. Only the pilot or controller mistakes varied.

The ultimate irony of Linate is that it had been equipped with surface radar, but had removed it to prepare for the installation of new equipment, components of which had been delivered as early as 1995. Linate acknowledged, in its original decision to install the old equipment, that it is particularly prone to thick fog and smog.

The technical inquiry in this case has a relatively simple job to do, but the judicial inquiry must dig deep into the political manoeuvrings which led to indecision over fitting the new radar system. The indecision was undoubtedly influenced by the debate over moving Milan's main airport from Linate to Malpensa, and even about Linate's continued existence. But that is not an excuse for removing an old, much-needed safety system and replacing it with nothing.

Source: Flight International