SMT ON TEST FLT TO CHK ENGS AND PRESSURIZATION DSNDS BELOW ASSIGNED ALT.

Narrative

ACFT ON A POST MAINT CHK FLT FOR PRESSURIZATION AND ENGS. CLB TO FL290 AND CRUISE UNEVENTFUL. DURING DSCNT; CTLR INITIALLY GAVE DSCNT TO FL260 THEN 13000 FT. BTWN FL260 AND FL200 CLRNC WAS REVISED TO FL190 AND ACKNOWLEDGED BY PLT AND SET INTO ALT ALERT SYS. PLT CONTINUED DSCNT AND WAS RECORDING ENG PARAMETERS AND MONITORING ENG; PRESSURIZATION; AND FLT INSTS. AT THIS POINT PLT BELIEVED HE WAS STILL CLRED TO 13000 FT. (ALT ALERT LIGHT FUNCTIONED; AURAL TONE DID NOT.) PLT SUDDENLY RECALLED CLRNC REVISION TO FL190 BUT BY THIS TIME ACFT HAD DSNDED TO FL180. PLT APPLIED CLB PWR AND STARTED RETURNING TO FL190 JUST AS ATC CALLED TO CONFIRM ALT CLRED TO. CONTRIBUTING FACTORS: SINGLE PLT WITH ONLY VISUAL ALT DURING ALERT (NO AURAL). EXCESSIVE RELIANCE ON AURAL ALT ALERT SYS. COMPLEX MISSION: TROUBLE-SHOOTING MULTIPLE SYS AND RECORDING RESULTS. PLT DISTRACTED FROM TASK AT HAND. PRIOR CLRNC TO A LOWER ALT ACKNOWLEDGED DURING A PEAK PERIOD OF COCKPIT ACTIVITY (I.E.; NOT FULLY IMPRESSED DESPITE ENTRY INTO ALT ALERT SYS). CLOSE IN TO LNDG SITE AND EXPECTATIONS FOR DSCNT WERE THERE. POOR PRIORITIES GIVEN TO THE TASKING THE PLT WAS ENCOUNTERING.