ALTDEV ALT EXCURSION FROM ASSIGNED.

Narrative

BOTH MY FO AND I WERE RESERVE AND CALLED AT THE LAST MINUTE TO FLY AN MD-11 FLT FROM MEM TO FLL ON JUN/XX/94. IT SHOULD BE NOTED THAT BOTH OF US HAD ONLY APPROX 2 HRS OF SLEEP PRIOR TO DEP. AFTER THE FLT WAS AIRBORNE FROM MEM; ZME CLRED THE FLT DIRECT FLL AT FL370. MY FO WAS AT THE CTLS ON THE LEG FROM MEM TO FLL. UPON BEING HANDED OVER TO ZMA AFTER APPROX 5 MINUTES ON THE 180 HDG; CTR CLRED THE FLT TO FORTL FOR THE FORTL TO ARR INTO FLL. MY FO 'INADVERTENTLY' TURNED THE ALT SELECTOR THINKING IT WAS THE HDG SELECTOR; THEN REALIZED WHAT HE HAD DONE AND CONTINUED HIS HAND ALONG THE GCP (GLARE SHIELD CTL PANEL); SELECTED THE HDG BUG TO PUT THE ACFT GOING TO FORTL AND THEN PUT HIS HEAD DOWN SO HE HAD TO GET INTO THE SECONDARY FLT PLAN ON THE FMS. THE ACFT WAS IN PROFILE AT THE TIME ALL THIS WAS TAKING PLACE. WHEN THE SECONDARY FLT PLAN PAGE ON THE FMS WAS ACTIVATED; THE ACFT STARTED A PROFILE DSCNT TO THE ALT THE FO HAD INADVERTENTLY SELECTED; WHICH WAS PART OF THE FORTAL 2 ARR ALREADY SELECTED IN THE FMS COMPUTER. THE ACFT DSNDED TO APPROX 35500 FT BEFORE I REALIZED WHAT HAD HAPPENED AND TOLD MY FO WE HAD NOT BEEN CLRED TO A LOWER ALT. HE THEN DISCONNECTED THE AUTOPLT; CLBED BACK TO FL370. WE TOLD ZMA AND THEY WERE VERY UNDERSTANDING AND PROFESSIONAL. A COMBINATION OF LACK OF SLEEP; A HIGH TECH AIRPLANE AND A BUSY ENVIRONMENT LED TO THIS ALTDEV. WE SHOULD HAVE CORRECTED THE INADVERTENT ALT SETTING RIGHT AWAY; BECAUSE THE COMPUTER IN PROFILE WILL DO EXACTLY WHAT THE PLT ASKED FOR WHEN IN THE PROFILE MODE. ALSO; I THINK THE COCKPIT CREW MUST BE VERY CAREFUL BEFORE USING THE SECONDARY FLT PLAN PAGE ON THE FMS. SUPPLEMENTAL INFO FROM ACN 272817: CONTRIBUTING FACTORS: BOTH PLTS HAD BEEN CALLED OUT ON RESERVE AT XX30 L. I WAS NOT AS SHARP AS I HOPE I WOULD HAVE BEEN WITH MORE REST. DISTR FROM MULTIPLE FLT PLAN CHANGES AT THE SAME TIME THE CAPT WAS BUSY WITH ARR CALLS. ON RESERVE FOR NEARLY A YR; MY PROFICIENCY AND RECENT EXPERIENCE IS NOT AT THE LEVEL I DESIRE.