CAPT OF A SAAB 340A (SF34-L) OVERSHOT ASSIGNED ALT AFTER TKOF DUE TO DISTR OF HAND FLYING THE ACFT AND LACK OF SLEEP. DEP CTLR INTERVENED AND ALERTED HIM AT 300 FT ABOVE ASSIGNED. THE FO WAS BUSY WITH AFTER TKOF CHKLIST.

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DURING THE CLB AFTER TKOF I CLBED BEYOND OUR INITIAL ALT ASSIGNMENT BY APPROX 300 FT. OUR ASSIGNED ALT WAS 2500 FT MSL. I WAS HAND FLYING WITHOUT THE FLT DIRECTOR OR AUTOPLT. WHEN THE ROCKFORD DEP CTLR VERIFIED OUR INDICATED ALT AND POS AFTER THE INITIAL CALL FROM THE FO THE ALT ERROR WAS NOTICED. I IMMEDIATELY STARTED A DSCNT BACK TO THE ASSIGNED ALT. DURING THE DSCNT WE WERE THEN CLRED TO 7000 FT MSL. I THEN BEGAN TO CLB AGAIN TO THE NEW ALT ASSIGNMENT. THERE WERE NO OTHER ACFT INVOLVED. CONTRIBUTING FACTORS AND HUMAN PERFORMANCE CONSIDERATIONS: I WAS PRIMARILY FOCUSED ON THE AIRSPD; ATTITUDE AND CLB RATE. I WAS NOT AS VIGILANT OF THE ACFT'S ALT AS AT MOST OF THE ARPTS THE INITIAL CLB ALT IS ABOVE 4000 FT MSL. I WAS TOO CONDITIONED TO THIS. THE FO WAS BUSY WITH THE AFTER TKOF CHKLIST AND DID NOT NOTICE THE ALT EXCURSION. IT DOESN'T TAKE US MUCH TIME TO GET TO 2500 FT. THE FLT WAS THE SECOND HALF OF A CONTINUOUS DUTY OVERNIGHT. WE ONLY HAD 4 HRS OF REST SINCE ARRIVING IN ROCKFORD AFTER XA00. THE FO AND FLT ATTENDANT BOTH SLEPT ON THE VAN RIDE FROM THE HOTEL TO THE ARPT. I WAS FORMULATING OPTIONS FOR AVOIDING THE LINE OF WX WE WOULD HAVE TO CROSS TO GET TO OUR DEST. I HAD AVERAGED ONLY 5 HRS OF SLEEP THIS MONTH DURING THE TRIPS. I WAS UNABLE TO GET CAUGHT UP ON REST DURING THE DAYTIME BTWN TRIPS. CONCLUSION: I NEED TO USE THE SYS THAT ARE AVAILABLE TO ME LIKE THE FLT DIRECTOR AND AUTOPLT. ESPECIALLY WHEN I AM SLEEP DEPRIVED AND FATIGUED. I TYPICALLY DID NOT USE THEM UNTIL CRUISE FLT. THIS IS DUE TO THE FACT THAT IT WOULD GET PRETTY BORING WATCHING THE AIRPLANE DO THE FLYING. I CAN DO WITHOUT THE ADRENALINE SHOT OF AN ALT EXCURSION HOWEVER. WHENEVER I AM AT AN ARPT WITH A LOWER THAN NORMAL INITIAL CLB RESTR I MUST BRIEF THIS WITH THE FO SO THAT WE CAN BOTH BE VIGILANT OF IT. PERHAPS THE CHKLIST CAN BE DELAYED UNTIL A BIT LATER WITHOUT COMPROMISING SAFETY.