While in a climb, air carrier was given a descent and issued traffic above him.

Attributes
ACN	111942
Time
Date	198905
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lax
State Reference	CA
Altitude	msl bound lower : 28000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Route In Use	enroute : direct
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 : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 6000
ASRS Report	111942
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 3000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We departed from san on a scheduled flight to oak. We were vectored off the peble 1 departure, and eventually given a 330 degree heading for lax. Then,direct gmn, direct pxn. Altitude assignment was FL350. Passing through FL286, and climbing at approximately 1500 FPM. ZLA direct us to level off at FL280, and called traffic at 12 O'clock, 1 1/2 mi, at FL290. I visually acquired the traffic and banked to the right as I reduced to idle power and began an immediate descent. The maximum altitude we reached was FL288, and we passed about 1/2 mi east of the traffic as we were descending through FL285. As soon as we were clear of the traffic, I advised ZLA that our assigned altitude had been FL350, and we were now descending to FL280. The controller said that he had initially given us FL350, but later changed that to FL280; and said something to the effect that 'there were a lot of aircraft on frequency.' neither the first officer nor myself heard, nor responded to, an altitude assignment of FL280--if one in fact had been given. After the incident, we did hear another aircraft with a (same #'south) 'east' 'C' call sign on the frequency, but to our knowledge, that was not a factor in the incident.

Original NASA ASRS Text

Title: WHILE IN A CLIMB, ACR WAS GIVEN A DESCENT AND ISSUED TRAFFIC ABOVE HIM.

Narrative: WE DEPARTED FROM SAN ON A SCHEDULED FLT TO OAK. WE WERE VECTORED OFF THE PEBLE 1 DEP, AND EVENTUALLY GIVEN A 330 DEG HDG FOR LAX. THEN,DIRECT GMN, DIRECT PXN. ALT ASSIGNMENT WAS FL350. PASSING THROUGH FL286, AND CLBING AT APPROX 1500 FPM. ZLA DIRECT US TO LEVEL OFF AT FL280, AND CALLED TFC AT 12 O'CLOCK, 1 1/2 MI, AT FL290. I VISUALLY ACQUIRED THE TFC AND BANKED TO THE RIGHT AS I REDUCED TO IDLE PWR AND BEGAN AN IMMEDIATE DSCNT. THE MAX ALT WE REACHED WAS FL288, AND WE PASSED ABOUT 1/2 MI E OF THE TFC AS WE WERE DSNDING THROUGH FL285. AS SOON AS WE WERE CLR OF THE TFC, I ADVISED ZLA THAT OUR ASSIGNED ALT HAD BEEN FL350, AND WE WERE NOW DSNDING TO FL280. THE CTLR SAID THAT HE HAD INITIALLY GIVEN US FL350, BUT LATER CHANGED THAT TO FL280; AND SAID SOMETHING TO THE EFFECT THAT 'THERE WERE A LOT OF ACFT ON FREQ.' NEITHER THE F/O NOR MYSELF HEARD, NOR RESPONDED TO, AN ALT ASSIGNMENT OF FL280--IF ONE IN FACT HAD BEEN GIVEN. AFTER THE INCIDENT, WE DID HEAR ANOTHER ACFT WITH A (SAME #'S) 'E' 'C' CALL SIGN ON THE FREQ, BUT TO OUR KNOWLEDGE, THAT WAS NOT A FACTOR IN THE INCIDENT.

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.