American Airlines Flight 5342, a regional jet en route from Wichita, Kan., was zooming down and about to land at Ronald Reagan National Airport in Washington on Wednesday night, when it made a last-minute turn upward.

Investigators with the National Transportation Safety Board appeared unsure if that meant that the pilots were alerted to something wrong in the plane’s final descent. But the sudden change in trajectory was not enough to avoid colliding with a military helicopter that was flying higher than it was supposed to be.

“I can tell you at one point very close to the impact, there was a slight change in pitch, an increase in pitch,” said Todd Inman, a member of the safety board.

In a briefing Saturday, members of the board provided new information and more detail than previously revealed of the moments leading up to the midair crash that proved to be the deadliest aviation accident in the United States in nearly a quarter of a century.

The regional jet and the Army Black Hawk helicopter collided between 300 feet and 350 feet above the ground over the Potomac River, according to the investigators who recovered information from the flight data recorders.

That places the helicopter more than 100 feet above the height that it was authorized to fly in its particular route near Reagan. Helicopters must fly at designated heights and remain in specific paths to avoid commercial airplanes coming in and out of the busy airport.

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