ALTDEV ALT OVERSHOT IN CLB.

Narrative

OUR COMPANY ACFT IS EQUIPPED WITH A FLT DIRECTOR; AND AN ALT ALERT WITH AN AURAL WARNING SYS. WE USUALLY SWITCH SEATS AFTER SEVERAL LEGS. THIS WAS MY LEG TO FLY BACK TO HOME BASE. SINCE WE ARE THE ONLY 2 PLTS FOR THE COMPANY; WE HAVE OUR ROUTINE OF THE COPLT DOING ALL OF THE CHART HANDLING; MAP READING; ETC. HOUSTON CTR GAVE US A CLB TO 7000 FT. WE ACKNOWLEDGED AND SET 7000 FT IN THE ALT ALERTER AS WE WERE CLBING THROUGH 3000 FT. I ASKED THE COPLT TO GET OUT THE ARR CHART FOR THE ACTON 2 ARR. AFTER A FEW MINS; I NOTICED HE WAS HAVING TROUBLE GETTING THE CHART BOOK OUT OF THE BOTTOM HOLDER LOCATED BEHIND HIS SEAT. I TURNED AROUND AND REACHED DOWN TO PULL IT OUT; WHICH DID NOT SEEM TO TAKE VERY LONG AT ALL. DURING THIS I HEARD THE ALT WARNING TONE GO OFF; THINKING THIS WAS THE TONE THAT USUALLY SOUNDS WHEN REACHING 1000 FT FROM THE ALT SET IN THE WINDOW. ABOUT THE SAME TIME THE CHART BOOK CAME OUT; I TURNED AROUND AND NOTICED WE WERE 800 FT ABOVE OUR ASSIGNED ALT OF 7000 FT. I IMMEDIATELY TURNED OFF THE AUTOPLT AND LOWERED THE NOSE TO RETURN TO THE ASSIGNED ALT OF 7000 FT. THE CTLR NEVER MENTIONED THE DEV; OF COURSE; NEITHER DID WE. SHORTLY AFTERWARDS WE WERE GIVEN A CLB TO 17000 FT; OUR REQUESTED ALT. AFTER GETTING HOME WE DISCUSSED THE CHAIN OF EVENTS LEADING UP TO THE ALTDEV. WE HAVE TALKED WITH OUR PART-TIME COPLTS AND HAVE DECIDED TO HAVE 1 PLT AT THE CTLS ALL THE TIME; NO MATTER WHAT THE COCKPIT DISTR MIGHT BE. WE ARE ALSO GOING TO HAVE ALT CALL-OUTS BY THE PNF.