Narrative:

As we were cleared onto runway 36 for takeoff at dca, tower told us to amend our initial altitude to 2000'. When we were switched over to departure control on 126.55, I reported climbing to 2000', stressing the 2000' since it was an unusual clearance. The controller immediately gave us clearance to 17000'. During this climb I was concerned about our track over the ground for the noise abatement departure, and said to the first officer, who was flying, that I thought he was too far south over roslyn. I then saw lights ahead of us that appeared to be getting closer. We leveled off somewhere between 2200 and 2400', and an aircraft flashed by on our right side. I would estimate the aircraft was several hundred ft horizontal distance, no more than 1/4 mi, and looked to be 100-300' above our altitude. I am convinced that had we been more directly over the potomac river on noise abatement track, and had not seen the aircraft to level off in time, we would have collided. As we were leveling off, and 3-4 seconds before the aircraft passed, the controller called us, but we missed what he said. Shortly afterward, the controller said it was an small aircraft and he had us in sight. I thought the small aircraft was at 2500', but 3 hours later, on our next arrival into dca, I called and talked to the departure control supervisor, who said the aircraft was an small aircraft at 3000' and was 'about 1 mi away.' I believe it was much closer than that.

Related reports:

Google
 

Original NASA ASRS Text

Title: CLOSE PROX ACR-LGT GA-SMA IN DCA TCA.

Narrative: AS WE WERE CLRED ONTO RWY 36 FOR TKOF AT DCA, TWR TOLD US TO AMEND OUR INITIAL ALT TO 2000'. WHEN WE WERE SWITCHED OVER TO DEP CTL ON 126.55, I RPTED CLBING TO 2000', STRESSING THE 2000' SINCE IT WAS AN UNUSUAL CLRNC. THE CTLR IMMEDIATELY GAVE US CLRNC TO 17000'. DURING THIS CLB I WAS CONCERNED ABOUT OUR TRACK OVER THE GND FOR THE NOISE ABATEMENT DEP, AND SAID TO THE F/O, WHO WAS FLYING, THAT I THOUGHT HE WAS TOO FAR S OVER ROSLYN. I THEN SAW LIGHTS AHEAD OF US THAT APPEARED TO BE GETTING CLOSER. WE LEVELED OFF SOMEWHERE BTWN 2200 AND 2400', AND AN ACFT FLASHED BY ON OUR RIGHT SIDE. I WOULD ESTIMATE THE ACFT WAS SEVERAL HUNDRED FT HORIZ DISTANCE, NO MORE THAN 1/4 MI, AND LOOKED TO BE 100-300' ABOVE OUR ALT. I AM CONVINCED THAT HAD WE BEEN MORE DIRECTLY OVER THE POTOMAC RIVER ON NOISE ABATEMENT TRACK, AND HAD NOT SEEN THE ACFT TO LEVEL OFF IN TIME, WE WOULD HAVE COLLIDED. AS WE WERE LEVELING OFF, AND 3-4 SECS BEFORE THE ACFT PASSED, THE CTLR CALLED US, BUT WE MISSED WHAT HE SAID. SHORTLY AFTERWARD, THE CTLR SAID IT WAS AN SMA AND HE HAD US IN SIGHT. I THOUGHT THE SMA WAS AT 2500', BUT 3 HRS LATER, ON OUR NEXT ARR INTO DCA, I CALLED AND TALKED TO THE DEP CTL SUPVR, WHO SAID THE ACFT WAS AN SMA AT 3000' AND WAS 'ABOUT 1 MI AWAY.' I BELIEVE IT WAS MUCH CLOSER THAN THAT.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.