International Desk || Radio interference linked to construction work at the White House prevented air traffic controllers from hearing routine warning calls from Marine One shortly before the helicopter carrying US President Donald Trump came dangerously close to a passenger aircraft near Ronald Reagan Washington National Airport on August 4, according to a preliminary report by the National Transportation Safety Board (NTSB).The incident occurred as Marine One was preparing to take off. Because controllers did not receive the usual three-minute advance warning, they cleared an Envoy Air passenger flight for takeoff at almost the same time.The NTSB said Marine One pilots had made the required warning calls, but recordings from the helicopter confirmed that the calls were not heard by the airport tower. The pilots later attempted to relay the warning through the helicopter base at Joint Base Anacostia-Bolling, but that effort also failed.The incident came after Marine One’s operating position had been moved because of construction at the White House. Technicians later identified intermittent communication problems between the helicopter and the tower.In response, the Federal Aviation Administration (FAA) moved a radio receiver from an area near the airport to the top of the Reagan National Airport tower. Subsequent tests showed that radio communications improved significantly after the change.Aviation safety expert Jeff Guzzetti said authorities had been aware of earlier communication problems but had failed to identify their underlying cause.The FAA said it took immediate action after the incident to improve communications between Marine One pilots and the airport by relocating the antenna.The NTSB found that the passenger aircraft and Marine One briefly came dangerously close to each other. The helicopter pilots spotted the aircraft and temporarily delayed takeoff until it had moved to a safe distance.Preliminary NTSB data showed that the aircraft came within about 1.3 kilometres horizontally and roughly 700 feet vertically of each other.Crew members of the Envoy Air flight told investigators that their traffic-alert system issued a warning shortly after takeoff, although they never saw the helicopter.The incident also appeared to violate safety procedures introduced after a mid-air collision near the busy airport last year that killed 67 people. Under a longstanding agreement between the Pentagon and FAA, controllers are supposed to receive a warning three minutes before the president’s helicopter takes off.Officials stressed that Trump was never in danger.Guzzetti said he did not blame the controllers because they never heard Marine One’s warning calls. Once they realised the helicopter was airborne, controllers quickly alerted the pilots and instructed another aircraft preparing to land at Reagan National to abort its approach and circle.The White House did not immediately comment on the preliminary report.