FLC OF AN SMA TRAINING ACFT INADVERTENTLY OVERSHOT DSCNT ALT ASSIGNMENT DUE TO INSTRUCTIONAL DISTR.

Narrative

WE WERE CONDUCTING ATTITUDE INST FLT TRAINING IN VFR CONDITIONS ABOVE SCATTERED/LAYERED CLOUDS. WE CALLED FOR AND RECEIVED A 'POP-UP' CLRNC TO LONG BEACH AND WERE TOLD TO DSND TO 4000 FT ON 090 DEG HDG (FROM 6500 FT). APCH CALLED AT 3000 FT THAT WE HAD BEEN TOLD TO MAINTAIN 4000 FT. WE IMMEDIATELY BEGAN A CLB BACK TO 4000 FT; AND HEARD ATC CALL US AS TFC TO AN AIRLINER. WE NEVER HAD VISUAL WITH HIM AS CLOUDS WERE SCATTERED AND LAYERED. I WAS INSTRUCTING A STUDENT BEGINNING INST TRAINING. WE WERE DSNDING AT 1000 FPM AND EXPLAINING WHAT ATC WAS DOING AND EXPECTING FROM US AS WE WERE DSNDING BACK TO LGB. IT WAS DISCOVERED BY ATC CALLING US TO MAINTAIN 4000 FT. CORRECTIVE ACTION IS TO ALWAYS CALL OUT TO YOURSELF FT- REMAINING-TO ASSIGNED ALT; PARTICULARLY 1000-TO-GO; 300- TO-GO; AND 100-TO-GO; AND NOT GET SO INVOLVED IN INSTRUCTING THAT YOU DON'T PAY ATTN TO ALT. ANOTHER CONTRIBUTING FACTOR WAS THE VMC CONDITIONS; AND I WAS LOOKING OUTSIDE AT UPCOMING CLOUDS AHEAD WHICH WE WOULD'VE BEEN IN RATHER THAN BELOW; IF WE'D LEVELED AT 4000 FT AS WE SHOULD HAVE SUBCONSCIOUSLY MAINTAINING VFR? ATC HAD QUERIED US ABOUT SKY CONDITIONS; POSSIBLY ANOTHER CONTRIBUTING FACTOR. (WE HAD EVEN WRITTEN DOWN THE ASSIGNED ALT; SO THAT IS NOT NECESSARILY INSURANCE AGAINST ALTDEVS!)