ATR42 CREW; DISTR BY COCKPIT PROC; OVERSHOT ALT ON DSCNT IN TJCS AIRSPACE.

Narrative

WE WERE CRUISING AT 16000 FT MSL WITH INSTRUCTIONS TO DSND AT PLT'S DISCRETION TO CROSS 30 NM SE OF SAN JUAN AT 11000 FT. AT ABOUT 50 DME; THE CAPT GAVE THE FO THE ACFT SO THAT HE COULD BRIEF THE APCH. IN ACCORDANCE WITH COMPANY POLICY; THE CAPT HAD LEFT 16000 FT IN THE AUTOPLT'S ALT WINDOW. AS THE APCH BRIEF WENT ON; THE FO SAW THAT THE ACFT WAS PRESSING CLOSE TO THE ALT RESTR(GPS/FMS INDICATED 1600 FPM REQUIRED AT CRUISE SPD) AND COMMENCED A DSCNT. THE CAPT NOTED THE DSCNT AND; AS AIRSPD INCREASED; DIRECTED 2100 FPM TO MAKE THE RESTR. NEITHER PLT REALIZED THAT THE AUTOPLT WAS STILL SET TO 16000 FT. WHEN THE CAPT TOOK THE CTLS BACK AT THE END OF HIS BRIEF; THE FO BRIEFED THE XFER; NOTING DSCNT IN PROGRESS TO 11000 FT. AT THAT TIME; THE FO SAW THAT THE AUTOPLT WAS STILL NOT SET AND BEGAN DIALING 11000 FT INTO THE ALT WINDOW. BEFORE THE FO GOT 11000 FT IN THE WINDOW; THE CAPT SAW THAT THE ACFT WAS ALREADY BLOWING THROUGH THE ASSIGNED ALT. THE CAPT DISENGAGED THE AUTOPLT AND BROUGHT THE ACFT BACK TO 11000 FT. ALT BOTTOMED OUT AT ABOUT 10600 FT. CONTRIBUTING FACTORS: 1) CREW DISTR DURING A TRANSITION (CAPT WITH APCH BRIEF; FO WITH LISTENING TO BRIEF; EVALUATING WX; ATC REQUESTS AND FLYING SIMULTANEOUSLY) -- LEADING TO BREAKDOWN IN CREW COORD/XCHKING. 2) COMPANY DOCTRINE WHICH SETS UP THIS TYPE OF ERROR AND RUNS COUNTER TO PLT HABIT PATTERNS. RECOMMENDATIONS: 1) FOR FO: CHANGE HABIT PATTERN FROM SETTING ALT WHEN ASSIGNED (THEN DSNDING WITH ASSUMPTION OF CORRECT SETTING) TO SETTING AND CHKING ALTS IMMEDIATELY PRIOR TO INITIATING ALT CHANGES. 2) FOR FO: INSIST THAT PNF PERFORM PNF TASKS (SUCH AS SETTING ALT) RATHER THAN REVERTING TO SINGLE PLT FLYING WHEN PNF IS BUSY. 3) FOR COMPANY: CHANGE POLICY TO ALLOW SETTING OF ALT WHEN ASSIGNED. IT NOT ONLY REMINDS CREW OF ALT CHANGE; BUT ELIMINATES THE POSSIBILITY OF THIS TYPE OF ERROR.