Narrative:

I was on the jumpseat performing a line check on the captain of this flight. Prior to descent into san; la center had the crew slow to slowest practical airspeed and gave them a late descent clearance causing them to be high on path for the BAYVU3 arrival. Shortly after passing lax; ATC vectored them off of the STAR to a heading of 090 and cleared them to FL200. There were multiple aircraft on the frequency with many non-standard instructions. Passing approximately FL300; ATC cleared the flight to turn right direct otiss and directed them to contact the next controller. Once again; the frequency was very busy with the controller handling many aircraft. The pilot monitoring (pm) checked in with their clearance to otiss and descending to FL200. As we were descending through FL235; ATC calls out crossing traffic from another carrier that was climbing to FL230. The next three events happened simultaneously. 1. The crew recognized that they were about to pass through the altitude that the called traffic was cleared to climb to and stopped their descent. 2. The controller asked them to verify their assigned altitude. 3. A TCAS TA was received. The pilot flying (PF) reversed his descent to a climb and climbed to FL240. ATC issued a clearance to maintain FL240. ATC issued a clearance to the other carrier to maintain FL200. Once the traffic conflict no longer existed; ATC cleared the flight to descend via the BAYVU3 arrival. Continued without incident.this was a very busy event. We talked about what happened and about possible errors made by all involved. Our best solution to prevent incidents like this in the future is to maintain an extra vigilance in the future when we encounter non-standard handling/vectors/clearances off of and onto RNAV stars and sids.

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Original NASA ASRS Text

Title: A B-737 Flight Crew and a Check Airman describe a TCAS TA event during which the crew took evasive action. ATC had pointed out the climbing traffic; but had not indicated there would be any conflict.

Narrative: I was on the jumpseat performing a Line Check on the Captain of this flight. Prior to descent into SAN; LA Center had the crew slow to slowest practical airspeed and gave them a late descent clearance causing them to be high on path for the BAYVU3 Arrival. Shortly after passing LAX; ATC vectored them off of the STAR to a heading of 090 and cleared them to FL200. There were multiple aircraft on the frequency with many non-standard instructions. Passing approximately FL300; ATC cleared the flight to turn right direct OTISS and directed them to contact the next Controller. Once again; the frequency was very busy with the Controller handling many aircraft. The Pilot Monitoring (PM) checked in with their clearance to OTISS and descending to FL200. As we were descending through FL235; ATC calls out crossing traffic from another carrier that was climbing to FL230. The next three events happened simultaneously. 1. The Crew recognized that they were about to pass through the altitude that the called traffic was cleared to climb to and stopped their descent. 2. The Controller asked them to verify their assigned altitude. 3. A TCAS TA was received. The Pilot Flying (PF) reversed his descent to a climb and climbed to FL240. ATC issued a clearance to maintain FL240. ATC issued a clearance to the other carrier to maintain FL200. Once the traffic conflict no longer existed; ATC cleared the flight to descend via the BAYVU3 Arrival. Continued without incident.This was a very busy event. We talked about what happened and about possible errors made by all involved. Our best solution to prevent incidents like this in the future is to maintain an extra vigilance in the future when we encounter non-standard handling/vectors/clearances off of and onto RNAV STARS and SIDS.

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.