The Army is pausing helicopter training flights around the Pentagon after a Black Hawk on Thursday forced two commercial airplanes to abort landings at Washington’s Ronald Reagan National Airport, three Army officials confirmed Monday.

U.S. Transportation Secretary Sean Duffy says it is “unacceptable” that two commercial aircraft had to abort landings at a Washington airport this week because of an Army Black Hawk helicopter that was flying to the Pentagon.

The episode followed a fatal collision between a military helicopter and a commercial jet in January, and prompted concern and outrage among officials.