U.S. Homeland Security Secretary Jeh Johnson says the man who landed a single-seat helicopter Wednesday on the grounds of the U.S. Capitol literally flew "under the radar."
A federal judge charged Doug Hughes, 61, Thursday with violating restricted airspace and illegally flying an unregistered aircraft.
Members of Congress, meanwhile, were demanding to know how it was possible for him to do what he did.
Johnson said Thursday that he wanted to "know all the facts" before deciding whether to change security procedures. But lawmakers from both parties said they were concerned about what they saw as a security gap.
Representative Elijah Cummings, a Maryland Democrat, said a "major catastrophe" could have occurred if there had been a bomb aboard the aircraft.
Republican Senator Lindsey Graham of South Carolina wanted to know why Hughes was not shot down for violating restricted airspace in Washington.
Johnson said no one wanted to overreact.
"We live in a democracy," he said. "We don't have fences around our airspace, so we've got to find out the right balance between living in a free and open society ... and the protection of federal buildings."
Hughes told the Tampa Bay Times newspaper that he wanted to carry out an act of civil disobedience to bring attention to campaign finance reform and what he said was government corruption.
He flew the small gyrocopter 132 kilometers from Gettysburg, Pennsylvania, straight into downtown Washington and settled a few hundred meters from the Capitol while stunned tourists watched. He was carrying letters to all 535 members of Congress.
A friend of Hughes tipped off the Secret Service about what Hughes was planning to do. An agent then interviewed Hughes at his Florida home and apparently determined that Hughes was not a threat, violent or suicidal.
Airspace around Washington has been highly restricted since the September 11, 2001, terrorist attack on the Pentagon and New York's World Trade Center. Any aircraft flying into the restricted zone risks being shot down.