Air carrier came in close proximity to another aircraft after departure.

Attributes
ACN	124966
Time
Date	198910
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : iad
State Reference	VA
Altitude	msl bound lower : 3600 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : initial
Route In Use	departure other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 20000 flight time type : 600
ASRS Report	124966
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	conflict : nmac non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was the captain and the PF iad to bos. We were cleared for takeoff by aid tower and instructed to maintain visibility sep with the aircraft that was launched just prior to us. His heading was 220 degrees assigned and we were assigned 240 degrees and to maintain 4000'. The takeoff runway was 19L. At about 2800' we were told to switch to departure. We first talked with departure control at about 3400' and checked in '3000 for 4000.' departure asked us to stop our climb at 3000'. We responded unable. I immediately initiated a level off and got level by 3600'. Within seconds we saw a third aircraft heading approximately north at 4000'. Approach asked us to turn north with no response about altitude. In my opinion, had we not leveled below 4000', we would have had a midair. The aircraft passed directly over the cockpit.

Original NASA ASRS Text

Title: ACR CAME IN CLOSE PROX TO ANOTHER ACFT AFTER DEP.

Narrative: I WAS THE CAPT AND THE PF IAD TO BOS. WE WERE CLRED FOR TKOF BY AID TWR AND INSTRUCTED TO MAINTAIN VIS SEP WITH THE ACFT THAT WAS LAUNCHED JUST PRIOR TO US. HIS HDG WAS 220 DEGS ASSIGNED AND WE WERE ASSIGNED 240 DEGS AND TO MAINTAIN 4000'. THE TKOF RWY WAS 19L. AT ABOUT 2800' WE WERE TOLD TO SWITCH TO DEP. WE FIRST TALKED WITH DEP CTL AT ABOUT 3400' AND CHKED IN '3000 FOR 4000.' DEP ASKED US TO STOP OUR CLB AT 3000'. WE RESPONDED UNABLE. I IMMEDIATELY INITIATED A LEVEL OFF AND GOT LEVEL BY 3600'. WITHIN SECS WE SAW A THIRD ACFT HDG APPROX N AT 4000'. APCH ASKED US TO TURN N WITH NO RESPONSE ABOUT ALT. IN MY OPINION, HAD WE NOT LEVELED BELOW 4000', WE WOULD HAVE HAD A MIDAIR. THE ACFT PASSED DIRECTLY OVER THE COCKPIT.

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.