C560XL IN DSCNT; ALTDEV ALT OVERSHOT. FO WAS WRITING NOTES AND PIC WAS LOOKING OUT THE WINDOW. NEITHER ONE HEARD THE ALT ALERTER AS THEY WERE WEARING HELMETS WITH PADDED HEADSETS.

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COMPLETED A SERIES OF TESTS IN THE BLOCK FL390-FL450 IN TEST AREA X. GIVEN A HDG APPROX 160 DEGS AND CLRED TO DSND TO FL370; WHICH WAS SET IN THE ALT SELECT WINDOW. I WAS PNF AND WAS 'CLEANING' UP MY NOTES (MAKING A FEW ADDITIONS) WHEN CTR ADVISED US THAT THEY ONLY HAD CLRED US TO FL370. I LOOKED UP AND WE WERE DSNDING THROUGH FL361. THE PLT PROMPTLY PITCHED UP AND LEVELED AT FL370. WHAT REALLY CAUSED THE PROB: WE WERE WEARING HELMETS; AND THEREFORE IT WAS DIFFICULT TO HEAR THE ALT ALERTER. THE COMPANY I FLY FOR DOES NOT STRESS CREW COORD; AND CALLOUTS 1000 FT PRIOR TO ALT ARE NOT REQUIRED. I WAS BUSY WRITING AND NOT WATCHING THE ALT. THE CAPT WAS LOOKING OUT THE WINDOW AND NOT WATCHING HIS INSTS. I SHOULD MORE OFTEN LOOK UP WHILE TAKING NOTES. THE COMPANY/MGMNT NEEDS TO STRESS THE IMPORTANCE OF CREW COORD AND ALT CALLOUTS AS THE AIRLINES DO. THE ONE PLT IN A 2 CREW COCKPIT MENTALITY NEEDS TO BE CHANGED. SUPPLEMENTAL INFO FROM ACN 362236: CREW WAS WEARING HELMETS DUE TO HAZARDOUS NATURE OF THE TEST. ALT ALERT NOT AUDIBLE WITH HELMETS ON. ALL AURAL ALERTS SHOULD PASS THROUGH BOTH SPEAKERS AND INTERCOM IN NEW ACFT DESIGNS.