C560 DSNDED 2000 FT BELOW CLRED ALT IN HOLDING PATTERN ENVIRONMENT.

Narrative

WHILE APCHING LAS ON THE LYNSY 2 ARR; WE WERE CLRED TO FL280 TO CROSS LYNSY INTXN AT 12000 FT. AFTER RECEIVING THIS CLRNC; MY FO LEFT THE FREQ TO OBTAIN THE CURRENT ATIS. WHILE IN THE DSCNT; CTR CALLED WITH INSTRUCTIONS TO HOLD AT LYNSY. NO EFC WAS GIVEN; SO I REQUESTED ONE TWICE. I THEN READ BACK THE HOLD POINT AND THE EFC. AT THIS POINT; MY FO CAME BACK ON AND I RELAYED THE HOLDING INSTRUCTIONS. AS WE WERE PASSING THROUGH 13000 FT; CTR REQUESTED OUR ALT. MY FO RESPONDED WITH OUR CURRENT ALT AND OUR 'CLRED TO' ALT OF 12000 FT. HE RESPONDED BY CLRING US TO 12000 FT AND INFORMED US WE HAD BEEN INSTRUCTED TO HOLD AT 15000 FT. AT LYNSY INTXN; WE WERE GIVEN A TURN TO A SOUTHERLY HDG. THE CTLR ADVISED US OF A POSSIBLE DEV AND TO CALL ZLA AFTER LNDG. DURING THE CALL TO SUPVR AT ZLA; I WAS INFORMED THE CTLR'S INSTRUCTIONS HAD INCLUDED AN ALT OF 15000 FT. I ASKED HIM IF THE TRANSCRIPT INDICATED IF I HAD RESPONDED TO THE ALT LIMITATION. HE CONFIRMED MY RESPONSE DID NOT INCLUDE THE ALT. I HAD ONLY RESPONDED TO THE HOLD FIX AND EFC. THIS ERROR WAS CAUSED BY IMPROPER CTLR PHRASEOLOGY AND FAILURE TO CONFIRM THE READBACK OF THE ALT RESTR GIVEN. SUPPLEMENTAL INFO FROM ACN 574755: ATC CLRED US DOWN TO FL280; CROSS LYNSY INTXN AT 12000 FT. ATC CANNOT JUST ASSUME THAT A FLT CREW HAS RECEIVED A NEW CLRNC; THEY HAVE TO GET A READBACK.