AN S80 FO HAS A PROB WITH HIS MODE CTL PANEL SET UP AND PORPOISES AROUND HIS ASSIGNED ALT WHILE ATTEMPTING TO ATTAIN 'BEST FORWARD SPD' IN ACCORD WITH CLRNC FROM ZAU; IL.

Narrative

LOCATION: BDF; FL240. CLRED TO FL230 AND BEST FORWARD SPD. FO USED IAS HOLD TO DSND AND ACCELERATE; UNAWARE ACFT CANNOT DO THIS WELL IN SHORT DSCNT. ACFT DEVELOPED BIG DSCNT RATE. I WARNED FO TO WATCH LEVELOFF. LEVELED AT FL228 AND STARTED CORRECTION WHEN CLRED TO FL210; BUT ACFT IN CAPTURE MODE DIRECTED BIG CLB WHICH FO FOLLOWED OVERSHOOTING TO FL235. I GAVE DIRECTION; DIRECTED HIM TO HAND-FLY; PULLED THROTTLES TO IDLE AND PUSHED OVER; BUT PEAKED OUT AT FL235. RETURNED SOLE CTL TO FO AND CONTINUED ARR GIVING INSTRUCTION AS I ANTICIPATED PROBS WITH NORMAL ORD ARR INSTRUCTIONS. NO OTHER PROBS; NO CALL FROM ATC; AND NO TFC ALERTS. CONTRIBUTING FACTORS: 1) STRONG FO SURPRISED ME WHEN HE GOT CONFUSED. I SHOULD HAVE TAKEN CTL EARLIER; BUT I THOUGHT MY INSTRUCTIONS WERE SUFFICIENT AT THE TIME. 2) FO CAME OFF 2 WK MIL LEAVE AND RECENT 6 MONTH MIL LEAVE. HE IS STILL RE-LEARNING THE LINE TECHNIQUES. 3) I HAVE 200 HRS AS CAPT AND THIS WAS MY FIRST PROB LIKE THIS. FO FELL BACK TO SCHOOLHOUSE PROCS IN A COMPLEX SIT. SUPPLEMENTAL INFO FROM ACN 489521: I STARTED THE DSCNT BY SELECTING VERT SPD OF 1000 FPM DOWN. IN THE DSCNT; CTR ASKED US TO GIVE THEM OUR BEST FORWARD SPD. SO I SELECTED IAS AND ROLLED IT TO 320 KIAS. THE NOSE DIPPED MORE THAN I EXPECTED AND WHEN THE ALT CAPTURED AT FL230; THE ACFT STILL HAD GOOD RATE OF DSCNT ON IT. I REALIZED THAT IT WAS GOING TO GO THROUGH FL230. I DESELECTED THE AUTOPLT AND BEGAN TO PULL THE NOSE BACK UP TO FL230. THE CAPT DIALED IN FL210 IN THE ALT WINDOW. I INCORRECTLY ASSUMED THAT THE V-BARS WOULD DIRECT ME TO FL210. I FORGOT THAT THE ALT HAD ALREADY CAPTURED FL230. WHILE CONCENTRATING ON THE V-BARS; WHICH WERE NOW DIRECTING A 500 FPM CLB; I CLBED BACK UP TO FL235; 500 FT ABOVE OUR PREVIOUSLY ASSIGNED FLT LEVEL. THE CAPT AND I DISCUSSED THE ERROR AND HE TOLD ME THE BETTER WAY TO HANDLE THIS SIT WAS TO SELECT THE INCREASED SPD WITH THE SPD SELECT AND SMOOTHLY CTL THE DSCNT WITH VERT SPD. I WAS PROBABLY A LITTLE BEHIND THE AIRPLANE AS WE WERE ENTERING THE BUSY ENVIRONMENT OF THE OHARE TFC AREA. BEING A RELATIVELY NEW HIRE WITH 300 HRS IN TYPE; I UNDERSTAND THE SEVERITY OF MY MISTAKE.