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A Bright Idea Becomes an FAA Rule December 2006
Imagine that you're a pilot taxiing out for takeoff at maximum gross weight. You're running through your final checklist, following the green taxiway centerline lights toward the runway, when suddenly you hear the tower barking "hold short, hold short!" … and you catch sight of an 900,000-lb 747 barreling toward you on the runway you've just started to cross. To prevent situations such as this, the FAA incorporated a new runway lighting scheme into its August 1, 2006, Airport Advisory Circular, changing the centerline taxiway lead-on lighting from all green to an alternating green and yellow pattern starting just beyond the runway hold-short line. Developed and evaluated by MITRE's Center for Advanced Aviation System Development and the FAA's William J. Hughes Technical Center, the new lighting scheme was designed to prevent runway incursions by creating an easily recognized visual cue to the pilot that the aircraft is about to enter the runway. It duplicates the lighting pattern that leads off the runway onto the taxiway, indicating the "no stop" segment that aircraft must pass through in order to be clear of the runway. Green and Yellow Mean "Caution" At night, under low light or foggy conditions, and at very wide taxiway intersections, vertical, painted signs can be hard to see. Even in ideal conditions, pilots who are busy with taxi or takeoff checklists may miss the indications that they are nearing the runway. What's more, the green centerline lights currently used on taxiways are visually indistinguishable from lead-on lights and can actually mislead pilots onto the runway. Runway incursions have been a major concern of the FAA over the past several years. Of the nation's 480 airports with control towers, 310 have reported at least one incident during the last decade. Between 1999 and 2005, there were more than 2,450 incursions, at least seven of which resulted in collisions. According to those involved, inability to clearly see the runway or its markings could have been a major factor. In fact, NASA's Aviation Safety Reporting System database contains reports from pilots who missed the entrance of runways and came close to incursions that they attributed to the lack of differentiation between the taxi and the runway environment. Lost on the Airfield In one incident, an arriving aircraft at Cleveland's airport missed slamming into a departing plane when it crossed a runway after being instructed to hold short. The flight crew reported that they had followed the green taxiway centerline lights and had not been able to see any indications for the runway environment. At San Francisco's airport, an aircraft departing at dusk entered a runway without authorization after taxiing on the wrong taxiway. The pilot stated that the lack of indication in the taxiway centerline lighting contributed to his error. Neither of those incidents resulted in serious consequences, but eight people died in Detroit in 1990 when a 727 on take-off roll was struck by another plane that had taxied onto the runway in dense fog. Though any of several factors may account for these incursions, it's a well established fact that pilots can get "lost" on an airfield, as happened in August 2006 when 49 people died because an aircraft took off from the wrong runway at a Kentucky airport. Though the present lighting system may not be to blame for this, modifying the lights can enhance pilots' situational awareness. In 2003, several FAA Lead Airport Certification Inspectors came up with a solution: changing the centerline taxiway lead-on lighting from all green to an alternating green-and-yellow pattern starting just beyond the hold short line. But what seems like a sure fix doesn't always work in reality, so the FAA decided to test the lighting scheme with a simulation and field demonstration before recommending it. In the summer of 2003, they asked MITRE to design and evaluate laboratory simulation studies and a field demonstration to test the effectiveness of this lighting scheme. Easily Seen In Low Light Using MITRE's Air Traffic Management Lab's cockpit simulator, 12 pilots performed a series of low visibility taxi operations on a simulated airfield. Most said that the green/yellow pattern would enhance awareness of the runway environment. At the same time, the FAA Tech Center in Atlantic City, New Jersey, conducted a parallel study that came to the same conclusions. In the summer of 2004, MITRE took this study into the field at Louisville, Kentucky's International Airport. Because UPS's air operations are based at the airport, there are extensive night operations, allowing a large number of pilots to view the new lighting configuration in the dark. Surveys designed by MITRE's human factors engineers were offered to all the pilots. Seventy-eight of them, whose average flight experience was 8,200 flight hours, completed the surveys. Eighty-five percent reported that the green/yellow lead-on lights enhanced awareness that they were approaching a runway. Even those who were very familiar with the airport reported that their situational awareness was improved by the modified lights. Another finding was that the modification did not affect aircraft taxi speed. System Impact An FAA Advisory Circular serves as a notice that the new lighting pattern must be incorporated into airports' lighting systems within six months of the circular's signing. About 40 airports have taxiway centerline lights, and for most this new lighting pattern will not be a difficult change by the early 2007 deadline. According to those who led the field evaluations, the cost of making the change is expected to be minimal. Work can be completed during regularly scheduled light-maintenance cycles and only a change of green filters to yellow filters is required. One of several ongoing FAA initiatives designed to improve runway safety, the change to green/yellow lead-on lights is a small, cost-effective step that can help prevent errors of enormous consequence. —by Faye Elkins Related Information Articles and News Technical Papers and Presentations
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