(CNN)  -- Federal investigators are concerned a potential danger persists because of the simultaneous use of intersecting runways at Newark Liberty International Airport, one of the nation's busiest and a gateway to the New York metro area. The alert comes after repeated instances in which planes above the Newark airport flew too close to each other in violation of safety standards. There were four such instances last year and at least four this year, according to the U.S. Department of Transportation inspector general. In one case, on January 16, 2008, two Continental planes -- a Boeing B-737 and an Embraer 145 -- missed each other by 600 feet, according to a DOT inspector general's report.
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Concerns cited about potential danger of using intersecting runways at Newark
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DOT inspector general: Planes above airport flew too close to each other repeatedly
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Air traffic controller says he was punished for raising safety issue with FAA
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FAA: Computer system that helps controllers stagger aircraft to be in use in December
She added, "@placeholder safety officers wanted to make absolutely sure employees were fully trained on the equipment."