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More than a year after USAir Flight 427 plunged from the sky near Pittsburgh, killing all 132 people aboard, the National Tranportation Safety Board will stage tests that might explain what triggered the 6,000-ft. nose dive, TIME's Jerry Hannifin reports. (The first test was schedule for today at the FAA's Flight Technical Center near Atlantic City, but was delayed because of bad weather.) Hannifin says the NTSB, under considerable pressure to solve the mystery behind the worst air disaster since 1987, is exploring an aeronautical phenomenon called wake vortex. Under a long-suspected scenario, the Boeing 737 jet might have run into air turbulence created by the jet that preceded it into Pittsburgh International Airport. "The four-mile separation may prove not to have been enough," Hannifin says. If the new tests produce evidence to substantiate the theory, he adds, the FAA could consider spacing planes farther apart on runways, despite the resulting delays.