Two commercial flights approaching Ronald Reagan National Airport were ordered to do “go-arounds” Thursday because of an Army helicopter, three months after a mid-air collision that killed 67 people, officials said.

U.S. Transportation Secretary Sean Duffy on Friday said he would demand answers from the Pentagon about the Black Hawk helicopter flight that forced the Delta Air Lines and Republic Airways planes to abandon their landings.

“Unacceptable. Our helicopter restrictions around DCA are crystal clear,” Duffy wrote on X, referring to airport by its Federal Aviation Agency location identifier.

No one was hurt in the incident, which occurred around 2:30 p.m.

U.S. Army spokesperson Capt. Victoria Goldfedib said that the UH-60 Black Hawk helicopter was “conducting flight operations into the Pentagon in accordance with published FAA flight routes and DCA Air Traffic Control” when it was told to go around by Pentagon Air Traffic Control.

The two commercial flights were then told to go around rather than land to ensure no conflicts in the airspace, Goldfedib said.

“The incident is currently under investigation. The United States Army remains committed to aviation safety and conducting flight operations within all approved guidelines and procedures,” she said.

The National Transportation Safety Board and the Federal Aviation ministration said they are investigating the incident.

The helicopter had no passengers, but two pilots and a crew chief were on board, two U.S. officials said. It was flying below 200 feet as it rehearsed a Joint Emergency Evacuation Plan, two officials told NBC, practicing approaches as part of the return to flight training operations.

Helicopters generally are not permitted to fly above 200 feet near Reagan, under FAA rules.

On Jan. 29, an American Eagle commercial plane and a Black Hawk helicopter collided in mid-air above the Potomac River near the airport, killing the 64 people aboard the jet and the three people aboard the helicopter.

The crash raised questions about the congested airspace around Ronald Reagan National Airport, which is in Arlington, Virginia, near Washington.

In that case, investigators have evidence that the helicopter involved in the mid-air collision was higher than the 200-foot ceiling, NTSB chair Jennifer Homendy said in February.

The NTSB has has said it wants to severely restrict helicopter traffic near the airport, arguing that there’s an “intolerable risk to aviation safety.”