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THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 1 OCTOBER 2005
ONLY evasive action "bordering on the heroic" and a large slice of luck prevented a clutch of collisions between passenger jets on the runways of some of the US's busiest airports this year.
So says Mark Rosenker, the head of the US air accident investigation body, the National Transportation Safety Board (NTSB). Rosenker claims the technology used to prevent runway collisions at US airports is putting lives at risk, because it is designed in such a way that pilots receive crucial warnings far too late.
Speaking at a conference on airport operations in Dulles, Virginia, on 13 September, he delivered a devastating critique of the measures taken to prevent so-called "runway incursions" that could lead to a collision. These happen at airports when aircraft, or aircraft and ground vehicles breach safe separation distances.
The world's worst ever plane crash was the result of a runway incursion. In 1977, two Boeing 747s collided on the Spanish island of Tenerife, killing 583 people, after a misunderstanding between the crew of a KLM aircraft and air traffic control. The KLM jumbo mistakenly thought it had clearance to take off on a runway where a Pan Am jumbo was already taxiing in heavy fog.
A spate of fatal accidents caused by runway incursions in the US in the late 1980s prompted the NTSB to act. It pressed the US aviation regulator, the Federal Aviation Administration, to improve air traffic control oversight of ground operations, pilot training, airport signs, runway lighting and runway markings.
"The FAA completed action on a number of important objectives to make the ground operation of aircraft safer," concedes Rosenker. "However, these runway incursion incidents continue to occur with alarming frequency." In 2004, the FAA reported 326 runway incursions at US airports, compared with 323 in 2003. Every month, two of these incursions were serious enough to have potentially caused an accident.
Numbers are similar in Europe. In European Union member states there is one runway incursion a day, according to the air traffic control agency Eurocontrol. And here again, serious incursions happen twice a month. The NTSB says the technology used to detect runway incursions and alert those involved needs to be significantly improved. Under fire is the Airport Movement Area Safety System (AMASS), which the FAA installed at 34 major US airports between 2001 and 2003.
AMASS uses an airport-wide ground radar system to detect the position of aircraft and ground vehicles. A computer compares the position, velocity and acceleration of all aircraft and vehicles and then works out when there is a potential conflict. When it predicts a breach of minimum separation between planes it automatically issues visual and audible alerts to air traffic control. Then it is up to the controller to warn the pilots that they need to take evasive action.
And therein lies the problem. The system relies on the controller getting the alert, deciding what to do and then warning the flight crew. But this takes crucial seconds that the flight crew may not have. The NTSB wants a system that provides a fast, direct warning to the pilots involved, not one mediated by a controller.
While the US has AMASS, Europe has the Advanced Surface Movement Guidance and Control System (ASMGCS), a similar system that merges data from ground radar and aircraft transponders and passes on the information to controllers rather than flight crew.
Paul Wilson, head of airport traffic management at Eurocontrol in Brussels, also believes a fast, cockpit-based warning system is needed. He says it takes just three to four seconds for an aircraft parked safely on a taxiway to roll onto the runway. If another aircraft is about to land, four seconds would not give a controller much time to alert the planes. "He's got to stop what he's doing, assimilate that information and work out a plan of action.Then the pilot has got to react to what they are told. We need a ground-based collision avoidance system for the pilots."
So Eurocontrol is going to investigate how such a system could work, on behalf of the UN's global aviation regulator, the International Civil Aviation Organisation (ICAO). It will begin drafting its "Action Plan for the Prevention of Runway Incursions" in early 2006. The draft will be circulated around the world for comment by pilots groups, controllers, airlines, airport operators and regulators.
Simple measures such as very clear runway signs and markings will form part of the plan, says Williams. The FAA is already developing a technology called Runway Status Lighting.
In RSL, a runway's state of readiness will be obvious from the colour of its lighting. A taxiway holding line lit up in red will mean "don't enter the runway", or red lights on the runway itself will mean "don't take off".
Tests in June at Dallas Fort Worth airport showed RSL could help pilots and tug drivers without increasing the air traffic controllers' workload, says the FAA. The system is automatic and receives data directly from AMASS.
The private sector is also developing technologies that will feed into the Eurocontrol study. Avionics company Honeywell makes the Enhanced Ground Protection and Warning System (EGPWS), which warns pilots when they are flying too low, or are about to hit a mountain. EGPWS has a detailed database of global terrain, including very fine detail for airports. So Honeywell has developed software to augment this, called the Runway Awareness and Alerting System, which gives taxiing pilots a raft of new detail about precisely where they are on the airport surface. Being in the wrong place plays a big factor in the errors that lead to incursions (see "Do you read me?", opposite).
There is no shortage of ideas, but action must be taken. Airlines cannot go on resolving near collisions through daring evasive action and pure luck, says Rosenker "That is not good enough."
AUTHOR: PAUL MARKS
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