Narrative:

We had an unexpected; abrupt altitude assignment immediately after takeoff to avoid a traffic conflict with another aircraft. Our TOGW was approximately 250;000 lbs assigned runway 9R; for a flaps 20 reduced EPR takeoff. The takeoff data message indicated it was an nadp-1 profile. Takeoff clearance included a 040 heading assignment. Takeoff through liftoff was uneventful. Immediately after engaging heading sel once safely airborne and gear retraction; I observed a B777 that appeared to be departing from runway 4R as either an initial takeoff or go-around. The B777 was in a right climbing turn; and was 500-1000 feet above us. Tower called out the traffic to us at 12:30 o'clock. Our turn toward 040 heading kept us clear from the B777 but tower told us to stop climb at 2;000 feet MSL; and a few seconds later amended to 2;100 feet. We were climbing through 900-1;000 feet when we received the instruction. The pilot monitoring captain set the MCP accordingly immediately; which went to. Speed and altitude capture. I had him to set a safe airspeed in the MCP. Soon afterwards tower assigned a heading of 360; then later 320. We stayed at 2;100 feet thru the turn. I was monitoring the autothrottle doing its best to keep our commanded airspeed as the indicated airspeed kept fluctuating close to the flaps 20 redline. While contrary to. Nadp-1 profile; I called for flaps 5 to alleviate overspeed concerns; but the captain left them at flaps 20 to keep the profile. Eventually we were cleared to a higher altitude and we cleaned up the flaps. We do not think we overspeeded the flaps. Rest of flight was uneventful.it is of concern to us why there was a B777 that appeared to be on a go-around or departure from runway 4R. It was in a right climbing turn; but initiation of that turn appeared to have started late; causing a conflict with us departing from runway 9R. Per the ATIS H we had; all arrivals and departures were on 9's and 10's. My opinion is that the B777 caught our tower controller off-guard as well (I think it was under a different person's control) and was forced to issue a level off instruction that was within 1;000 feet of our altitude during a takeoff climb.

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Original NASA ASRS Text

Title: B757 First Officer reported abrupt ATC altitude assignment due to airborne conflict shortly after takeoff.

Narrative: We had an unexpected; abrupt altitude assignment immediately after takeoff to avoid a traffic conflict with another aircraft. Our TOGW was approximately 250;000 lbs assigned Runway 9R; for a Flaps 20 reduced EPR takeoff. The takeoff data message indicated it was an NADP-1 profile. Takeoff clearance included a 040 heading assignment. Takeoff through liftoff was uneventful. Immediately after engaging HDG SEL once safely airborne and gear retraction; I observed a B777 that appeared to be departing from Runway 4R as either an initial takeoff or go-around. The B777 was in a right climbing turn; and was 500-1000 feet above us. Tower called out the traffic to us at 12:30 o'clock. Our turn toward 040 heading kept us clear from the B777 but Tower told us to stop climb at 2;000 feet MSL; and a few seconds later amended to 2;100 feet. We were climbing through 900-1;000 feet when we received the instruction. The Pilot Monitoring Captain set the MCP accordingly immediately; which went to. SPD and ALT CAPTURE. I had him to set a safe airspeed in the MCP. Soon afterwards Tower assigned a heading of 360; then later 320. We stayed at 2;100 feet thru the turn. I was monitoring the Autothrottle doing its best to keep our commanded airspeed as the indicated airspeed kept fluctuating close to the Flaps 20 redline. While contrary to. NADP-1 profile; I called for Flaps 5 to alleviate overspeed concerns; but the captain left them at Flaps 20 to keep the profile. Eventually we were cleared to a higher altitude and we cleaned up the flaps. We do not think we overspeeded the flaps. Rest of flight was uneventful.It is of concern to us why there was a B777 that appeared to be on a go-around or departure from Runway 4R. It was in a right climbing turn; but initiation of that turn appeared to have started late; causing a conflict with us departing from Runway 9R. Per the ATIS H we had; all arrivals and departures were on 9's and 10's. My opinion is that the B777 caught our Tower Controller off-guard as well (I think it was under a different person's control) and was forced to issue a level off instruction that was within 1;000 feet of our altitude during a takeoff climb.

Data retrieved from NASA's ASRS site 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.