F27 CREW HAD AN ALTDEV WHILE APCHING SBA.

Narrative

THE CAPT AND I WERE FLYING ACFT INTO SBA ARPT ON OUR REGULAR SCHEDULED RUN FROM ONT DIRECT SBA. THE CAPT WAS THE PF ON THIS LEG. WE WERE TALKING WITH POINT MUGU ON FREQ 128.65. I WAS TRYING TO GET THE ATIS FOR SBA WHILE ALSO LISTENING TO MUGU APCH. MUGU APCH KEPT POINTING OUT TFC FOR US TO LOOK FOR. THIS MADE IT IMPOSSIBLE FOR ME TO GET THE ATIS FOR SBA. WE WERE THEN HANDED OFF TO SBA APCH. SINCE WE DID NOT HAVE THE ATIS; I ASKED THE CAPT TO COVER THE #1 FREQ WHILE I LISTENED TO THE ATIS FREQ 132.65 AT SBA. HE REPLIED THAT HE HAD #1. AFTER I HAD FINISHED GETTING THE ATIS; I RETURNED MY RADIO TO #1 FREQ AND TOLD THE CAPT THAT I WAS BACK ON #1 RADIO. THE CAPT THEN INFORMED ME THAT WE WERE CLRED FOR THE VISUAL APCH TO RWY 25 AT SBA. I REPLIED AFFIRMATIVE AND GAVE HIM ATIS INFO AT SBA. AS WE DSNDED TO 4600 FT MSL THE CTLR AT SBA TOLD US THAT WE WERE SUPPOSED TO MAINTAIN 6000 FT MSL; TO WHICH THE CAPT REPLIED TO ME 'NO; WE WERE CLRED FOR THE VISUAL.' AFTER BEING CLRED FOR THE VISUAL TO RWY 25 AT SBA; IT WAS LATER DISCOVERED THAT THE PREVIOUS CLRNC GIVEN TO THE CAPT WAS TO PROCEED VISUALLY TO THE ARPT BUT TO MAINTAIN 6000 FT MSL. THIS WAS LATER CONFIRMED BY THE CAPT'S OWN VOICE RECORDER WHICH HE HAS IN HIS POSSESSION AND LISTENED TO IN FRONT OF ME.