Ongoing work at the White House may have contributed to a near-collision between the presidential helicopter Marine One and a commercial airliner over Washington earlier this month, a National Transportation Safety Board (NTSB) report found.

The close encounter occurred on August 4 after President Donald Trump departed aboard Marine One from a temporary pad on the Ellipse outside the White House complex, while a permanent helipad was being built inside the grounds. Both the White House and the Federal Aviation Administration (FAA) said Trump was never in danger.

NTSB investigators determined that air-traffic controllers at Washington’s Ronald Reagan National Airport did not receive the first radio transmission notifying them of the helicopter’s imminent departure, and that the second attempt was degraded and completely unintelligible.