President Donald Trump ’s giant “triumphal arch” is under evaluation by the Federal Aviation Administration for potential risks to flights near one of the country’s busiest airports, according to a new report. The proposed 250-foot arch would be built at the end of Arlington Memorial Bridge, across from the Lincoln Memorial. The massive structure is expected to sit less than two miles from Ronald Reagan Washington National Airport, potentially posing a danger to flights into the D.C. area . Trump’s Interior Department has requested a formal aeronautical study from the FAA for the arch, CNN reported Tuesday. According to federal regulations, the FAA must be notified of any construction more than 200 feet. The FAA told the outlet it had begun the study. But it’s unclear how long it will take.…