RVSM May Not Be Safe


Squeezing more planes into less space (and using technology to keep them apart) may not be as safe as proponents of Reduced Vertical Separation Minima (RVSM) claim. Peter Ladkin, a computer scientist specializing in “dependable systems” at Germany’s University of Bielfeld told NewScientist.com that reducing vertical separation from 2,000 feet to 1,000 feet doesn’t leave much wiggle room for pilots who have to take evasive action when their collision avoidance systems go off. In fact, he claims Eurocontrol, the pan-European air traffic control organization, ignored several incidents and accidents involving sudden altitude changes when it compiled its safety research. Eurocontrol officials deny Ladkin’s claim, saying the ability of modern aircraft to maintain their height precisely keeps them safely separated. Ladkin says the planes themselves may be models of precision but when things go wrong — and humans have to take over — all that accuracy goes out the window. He said he’s particularly concerned about the reaction of pilots and controllers to the warnings issued by the Airborne Collision Avoidance systems (ACAS) on newer aircraft. Ladkin cited three mishaps, a midair collision and two near-collisions, in which the 1,000 feet clearly wasn’t enough. “I don’t think we yet understand the behavioral side of ACAS interactions well enough to guarantee safety under RVSM,” he said. Eurocontrol maintains that the collision rate resulting from RVSM will be one every 150 years but Ladkin says that’s optimistic, given the holes he found in the supporting data.