Washington (CNN) -- A commercial jetliner and a military helicopter came dangerously close near Washington's Reagan National Airport in an incident now being investigated by the Federal Aviation Administration and the National Transportation Safety Board.
The two aircraft came "extremely close" -- flying at the same altitude and within 950 feet of each other laterally -- causing an audible alert in the jetliner's cockpit, and prompting the pilot to abort the landing and circle around for another landing, said NTSB spokesman Eric Weiss.
Both aircraft landed safely.
The jetliner, Republic Airlines Flight 3281 originating in Columbus, Ohio, was northbound, descending to Runway 33 at Reagan National Airport about 4:05 p.m. Friday, FAA spokeswoman Laura Brown said in a statement.
The southbound helicopter was flying on "helicopter route 4," on the east side of the Potomac River. Both aircraft were on the same radio frequency and the two pilots had each other in sight, Brown said.
The controller told the helicopter pilot to pass below and behind the passenger jet, which the helicopter confirmed he would do, Brown said.
The pilot of the helicopter had "briefly climbed" to the altitude of 400 feet at the same time the passenger aircraft passed that altitude on descent, Brown said.
The two aircraft came closest about one mile south of the airport, Brown said.
After Republic's collision avoidance system sounded, the jet circled around and landed safely a few minutes later, officials said.
Brown and Weiss said the helicopter is based at Joint Base Andrews on the outskirts of Washington.
The weather was good, and is not believed to be a factor in the incident.