Air carrier departing LAX Runway 24L was instructed to maintain visual separation from a 25R departure; elected to turn from assigned heading to secure separation and was questioned by ATC.
Synopsis
Air carrier departing LAX Runway 24L was instructed to maintain visual separation from a 25R departure; elected to turn from assigned heading to secure separation and was questioned by ATC.
Narrative
We were given position and hold 24L at LAX. Tower asked if we had Air Carrier Y departing 25R in sight. I told him that we did not. He then gave us a takeoff clearance. I read back the clearance and told him that we now have the traffic in sight. He then asked us to maintain visual separation. After switching to Departure and receiving a climb clearance to 13;000; we continued the climb. Passing around 5000 ft; Departure gave the preceding Air Carrier Y a turn that would cross our departure path. I had lost sight of that aircraft under our nose; but the Captain still had visual. It appeared to him that; given our close proximity (approximately 2.5 miles on the TCAS display); we may have a loss of separation and possible safety concern. As the Captain began to deviate from our departure heading; I asked Departure for another heading to avoid a conflict. He told us that we were still 3 miles in trail (with no conflict) and to ask for the heading BEFORE turning. We explained that from our vantage point (and very close proximity); a conflict could have easily happened. Air Carrier Y continued its turn to the north and we continued our straight out climb with no conflict. I understand that ATC gives clearances with the information they have on their radar scopes and that info is very accurate. I also believe that it is ultimately our responsibility as Pilots for the safe conduct of our flight. With a visual separation clearance; it was our responsibility to avoid hitting the preceding aircraft and I believe we did exactly that.
Second reporter narrative
We took off 24L in LAX with a clearance to maintain runway heading. Air Carrier Y took off 25R and we were asked to maintain visual with the departing Air Carrier. As we were climbing out; Air Carrier Y was ahead and to the left of us by about 2.5 miles and 1500 FT or so above. We were climbing at 2500 FT a minute when ATC gave Air Carrier Y a right turn to 280; which brought it across our flight track. I elected to turn to 280 heading as well to parallel the traffic until I could slow my climb rate down to ensure that I could pass under Air Carrier Y . The First Officer was attempting to contact ATC to let them know we have turned. Once we were sure we could pass under Air Carrier Y; we turned back to our assigned heading. ATC was concerned that we had turned without telling them; but we explained that we had to maintain visual on the aircraft ahead; which meant turning until we could ensure we passed below Air Carrier Y. There was no loss of separation from any aircraft. Maybe the ATC guys can provide a little more separation on departing aircraft when they are going to cross paths. We called TRACON and explained what happened and why.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.