Narrative:

In cruise flight at FL370 and in the vicinity of lax VOR, we received the following clearance: 'descend to FL240, expect cardi at 15000 ft. Expect lower (shortly/in a few mins) reference traffic.' I acknowledged that clearance and the first officer agreed with what I had read back. We began our descent to FL240. Approaching FL350, ZLA requested our altitude. I responded 'passing FL355 for FL240.' center responded that we had been given an expect clearance and to turn left 20 degrees for traffic. He then called a second aircraft and told him to turn left 20 degrees. About this time we noticed an aircraft at FL350 just inside the scope of our TCASII. We never got close enough to that aircraft to get any TCASII alerts or warnings. I estimate that he passed about 10 mi west of us. I called ATC to confirm the altitude he wanted us to maintain and then asked for a phone number that I could call after I landed. I talked to a ZLA supervisor after landing and he basically said 'no harm, no foul.' I asked if he had reviewed the tapes and he said that he had not, but had been briefed to expect my call. I told him what I had heard and he agreed it was at the least a very odd clearance. He reiterated that there had not been a problem and that he would review the tape for their future training sessions. I am 99.9% sure of the clearance I received and 100% sure of what I read back. I think this is a classic example of why it is imperative for ATC to be responsible for assuring that the clearance the pilot reads back to them is the clearance that ATC actually intended to be issued.

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Original NASA ASRS Text

Title: FLC OF A B737 STARTED DSCNT PER ARTCC CTLR CLRNC AND THEN SHORTLY STOPPED BY CTLR AND TURNED TO AVOID TFC. CTLR ADVISED THAT THE DSCNT CLRNC WAS EXPECT ONLY.

Narrative: IN CRUISE FLT AT FL370 AND IN THE VICINITY OF LAX VOR, WE RECEIVED THE FOLLOWING CLRNC: 'DSND TO FL240, EXPECT CARDI AT 15000 FT. EXPECT LOWER (SHORTLY/IN A FEW MINS) REF TFC.' I ACKNOWLEDGED THAT CLRNC AND THE FO AGREED WITH WHAT I HAD READ BACK. WE BEGAN OUR DSCNT TO FL240. APCHING FL350, ZLA REQUESTED OUR ALT. I RESPONDED 'PASSING FL355 FOR FL240.' CTR RESPONDED THAT WE HAD BEEN GIVEN AN EXPECT CLRNC AND TO TURN L 20 DEGS FOR TFC. HE THEN CALLED A SECOND ACFT AND TOLD HIM TO TURN L 20 DEGS. ABOUT THIS TIME WE NOTICED AN ACFT AT FL350 JUST INSIDE THE SCOPE OF OUR TCASII. WE NEVER GOT CLOSE ENOUGH TO THAT ACFT TO GET ANY TCASII ALERTS OR WARNINGS. I ESTIMATE THAT HE PASSED ABOUT 10 MI W OF US. I CALLED ATC TO CONFIRM THE ALT HE WANTED US TO MAINTAIN AND THEN ASKED FOR A PHONE NUMBER THAT I COULD CALL AFTER I LANDED. I TALKED TO A ZLA SUPVR AFTER LNDG AND HE BASICALLY SAID 'NO HARM, NO FOUL.' I ASKED IF HE HAD REVIEWED THE TAPES AND HE SAID THAT HE HAD NOT, BUT HAD BEEN BRIEFED TO EXPECT MY CALL. I TOLD HIM WHAT I HAD HEARD AND HE AGREED IT WAS AT THE LEAST A VERY ODD CLRNC. HE REITERATED THAT THERE HAD NOT BEEN A PROB AND THAT HE WOULD REVIEW THE TAPE FOR THEIR FUTURE TRAINING SESSIONS. I AM 99.9% SURE OF THE CLRNC I RECEIVED AND 100% SURE OF WHAT I READ BACK. I THINK THIS IS A CLASSIC EXAMPLE OF WHY IT IS IMPERATIVE FOR ATC TO BE RESPONSIBLE FOR ASSURING THAT THE CLRNC THE PLT READS BACK TO THEM IS THE CLRNC THAT ATC ACTUALLY INTENDED TO BE ISSUED.

Data retrieved from NASA's ASRS site as of July 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.