Narrative:

Descending into stl, we were cleared from FL310 to FL290. Copilot flying, the autoplt engaged descending and the autoplt altitude arm was armed to capture FL290. Somehow approaching FL290, the altitude arm was disengaged because the airplane descended through FL290. The altitude alert sounded 250 ft below FL290. The first officer disengaged the autoplt with his thumb switch and stopped the descent abruptly and began a climb. However, he over-controled his pullup and climbed too fast and was not able to level the aircraft at FL290. He was above the altitude by about 200 ft at which time I said 'I have the airplane.' he did not release his hold on the yoke and I then yelled, '..... Let go now, I have the airplane.' we were approximately 300 ft above FL290 before I took the aircraft and descended back to FL290. This first officer has what I think is a bad habit of keeping his left hand on the turn knob and glare shield in between heading inputs which makes it very difficult for me to see what he does when he makes inputs to the autoplt. Some way he disengaged the altitude arm by making an input he did not realize, and I did not catch it until the altitude alert sounded. I am seeing a number of my first officer's on the md-80 aircraft who are unable to fly the aircraft manually above 10000 ft or on descent from high altitudes (above 30000 ft). Our company teaches them to use the autoplt in performance climb or performance descent modes and they are losing their ability to hand fly the aircraft. Once the autoplt goes in altitude capture (which can happen several hundred ft about armed altitude, depending on sink rate) any input to vertical speed, IAS, or mach speed can disengage altitude capture.

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Original NASA ASRS Text

Title: FLC OF AN MLG OVERSHOT DSCNT ALT DUE TO AUTOPLT ALT CAPTURE OFF AND THEN OVERCORRECTED BACK OVERSHOOTING THE TARGET ALT.

Narrative: DSNDING INTO STL, WE WERE CLRED FROM FL310 TO FL290. COPLT FLYING, THE AUTOPLT ENGAGED DSNDING AND THE AUTOPLT ALT ARM WAS ARMED TO CAPTURE FL290. SOMEHOW APCHING FL290, THE ALT ARM WAS DISENGAGED BECAUSE THE AIRPLANE DSNDED THROUGH FL290. THE ALT ALERT SOUNDED 250 FT BELOW FL290. THE FO DISENGAGED THE AUTOPLT WITH HIS THUMB SWITCH AND STOPPED THE DSCNT ABRUPTLY AND BEGAN A CLB. HOWEVER, HE OVER-CTLED HIS PULLUP AND CLBED TOO FAST AND WAS NOT ABLE TO LEVEL THE ACFT AT FL290. HE WAS ABOVE THE ALT BY ABOUT 200 FT AT WHICH TIME I SAID 'I HAVE THE AIRPLANE.' HE DID NOT RELEASE HIS HOLD ON THE YOKE AND I THEN YELLED, '..... LET GO NOW, I HAVE THE AIRPLANE.' WE WERE APPROX 300 FT ABOVE FL290 BEFORE I TOOK THE ACFT AND DSNDED BACK TO FL290. THIS FO HAS WHAT I THINK IS A BAD HABIT OF KEEPING HIS L HAND ON THE TURN KNOB AND GLARE SHIELD IN BTWN HDG INPUTS WHICH MAKES IT VERY DIFFICULT FOR ME TO SEE WHAT HE DOES WHEN HE MAKES INPUTS TO THE AUTOPLT. SOME WAY HE DISENGAGED THE ALT ARM BY MAKING AN INPUT HE DID NOT REALIZE, AND I DID NOT CATCH IT UNTIL THE ALT ALERT SOUNDED. I AM SEEING A NUMBER OF MY FO'S ON THE MD-80 ACFT WHO ARE UNABLE TO FLY THE ACFT MANUALLY ABOVE 10000 FT OR ON DSCNT FROM HIGH ALTS (ABOVE 30000 FT). OUR COMPANY TEACHES THEM TO USE THE AUTOPLT IN PERFORMANCE CLB OR PERFORMANCE DSCNT MODES AND THEY ARE LOSING THEIR ABILITY TO HAND FLY THE ACFT. ONCE THE AUTOPLT GOES IN ALT CAPTURE (WHICH CAN HAPPEN SEVERAL HUNDRED FT ABOUT ARMED ALT, DEPENDING ON SINK RATE) ANY INPUT TO VERT SPD, IAS, OR MACH SPD CAN DISENGAGE ALT CAPTURE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.