Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 110; Flight Crew Type 14000
Human-Machine Interface
Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action
Environment - Non Weather Related; Human Factors; Procedure
SNA Tower cleared us for takeoff on 20R but changed our clearance altitude from 5;000 feet to 3;000 feet for crossing traffic. We were very light and the max power setting gave us a very very high climb rate. We had a LEVEL OFF RA at 2;800 feet MSL which was the easy part. We complied and did not go above 3;000 feet as a light aircraft passed directly overhead. I believe the separation was 400 feet. Complicating this situation; and the real reason for this report; was the fact that we were given a 3;000 feet clearance and our performance was so high; we got ALT ACQ around 1;000 feet. Our automation did not provide proper guidance as the speed reverted to flaps up speed (15) and the autothrottles wanted to go to max power (takeoff power 100.6%). Also; the cutback N1 was 26% less than takeoff power! My FO had to disconnect the Autothrottles to prevent them from surging back to max power after he set them to cutback and flight directors were commanding a climb well above 10-15 degrees even though my speed was below the shark tooth. I had to fly out of the situation and my FO gave great communication as he kept our SA in focus. I am not 100% sure what happened with the automation but I believe the ALT ACQ at such a low altitude caused some serious issues. This would not have happened with a normal 5;000 feet clearance; or if we were heavy with less performance or we were doing a normal takeoff profile.However; I am concerned that with a few more variables or a crew that did not work as effectively as we did today this could have been a much worse outcome. I am wondering if we should be given 3;000 feet clearances with crossing traffic. With a normal takeoff profile it would have been fine but the max power setting and with the large power cutback for noise abatement this was a tricky situation. Compliments to my FO who took action on the autothrottles to prevent an automated max thrust climb after he pulled for cutback by disengaging them and clearly communicating that part of the problem.
Air carrier Captain reported an NMAC during takeoff from SNA airport.  Captain cited a high climb rate due to the aircraft being light in weight and a last minute lowered altitude crossing restriction contributed to the event.