THE AUTOPLT WAS UNINTENTIONALLY ENGAGED ON A DHC-8.

Narrative

WHILE HAND FLYING THE ACFT ON A VISUAL APCH TO CLT RWY 18R; I EXPERIENCED A ROLL CTL JAM; OR WHAT APPEARED TO BE A CTL JAM; WHEN I ATTEMPTED TO ROLL OUT OF A 30 DEG R BANK AS I INTERCEPTED THE FINAL APCH HDG. AFTER BOTH THE FO AND I TRIED TO OVERPWR THE CTL JAM BRIEFLY; I DISCONNECTED THE ROLL CTLS IN ACCORDANCE WITH DHC-8 PROCS. HOWEVER; IMMEDIATELY AFTER I DISCONNECTED THE CTLS AND MY YOKE BECAME FREE; THE FO'S YOKE BROKE FREE. THE AP/YD (AUTOPLT/YAW DAMPER) FAIL ANNUNCIATOR ILLUMINATED ON MY FLT GUIDANCE ADVISORY PANEL INDICATING TO ME THAT THE AUTOMATIC FLT CTL SYS (POSSIBLY AUTOPLT) WAS IN SOME WAY INVOLVED. AFTER A NORMAL LNDG WITH THE ROLL CTLS RE-ENGAGED AND FULLY FUNCTIONAL; NO MECHANICAL DISCREPANCY OR FOREIGN OBJECT DAMAGE COULD BE FOUND IN THE ROLL CTL SYS. MAINT TESTED THE AUTOPLT ON THE GND AND IT WAS BELIEVED THAT THE AUTOPLT HAD BECOME ENGAGED. INITIALLY MAINT ACCEPTED THE IDEA THAT ITS ENGAGEMENT WAS DUE TO A SPURIOUS SIGNAL; BUT LATER EXAMINATION OF FLT DATA RECORDS INFO LED TO THE ASSUMPTION BY MGMNT THAT I HAD INADVERTENTLY AND UNKNOWINGLY ENGAGED THE AUTOPLT WHEN REACHING FOR THE APCH MODE SELECTOR ON FLT GUIDANCE CTL PANEL. I HONESTLY DON'T BELIEVE THAT THIS IS WHAT HAPPENED; BUT THERE IS A STRONG TENDENCY FOR THAT EXACT ERROR TO OCCUR AS THE 2 BUTTONS ARE RIGHT BESIDE EACH OTHER AND THERE IS NO OTHER ANNUNCIATION OF AUTOPLT ENGAGEMENT EXCEPT AT THE ENGAGEMENT BUTTON WHICH IS IN THE CTR OF THE GLARE SHIELD; OUT OF BOTH PLT'S SCAN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR BELIEVES THAT MOST PLTS THAT FLY THE DHC-8 HAVE INADVERTENTLY TURNED ON THE AUTOPLT AS ITS BUTTON IS VERY NEAR THE 'APCH MODE' SELECTOR BUTTON ON THE MODE CTL PANEL. ON THE NON-EFIS DHC-8 ACFT; THERE IS NO WARNING THAT THE AUTOPLT HAS BEEN DISCONNECTED EITHER INTENTIONALLY OR INADVERTENTLY. THE ONLY INDICATION THAT THE AUTOPLT IS ON IS A SMALL ILLUMINATED ARROW IN THE SELECTOR BUTTON ITSELF THAT IS NOT READILY IN SIGHT. THE DHC-8 ACFT OCCASIONALLY HAS 'ELECTRONIC GLITCHES' WHEREIN THE AUTOPLT OR OTHER ITEMS SEEM TO BE ABLE TO TURN THEMSELVES ON OR OFF WITHOUT WARNING. IT IS VERY POSSIBLE TO TURN ON THE AUTOPLT WHEN REACHING FOR THE APCH MODE SELECTOR; ESPECIALLY IN TURBULENT AIR. BOTH THE FAA AND THE NTSB HAVE BEEN INFORMED OF THIS INCIDENT. THE FLC RECEIVED SOME ADDITIONAL TRAINING IN COCKPIT RESOURCE MGMNT. THE ROLL CTL DISCONNECT THAT THE RPTR REFERS TO IS A 'T' HANDLE ON THE CONSOLE THAT DISCONNECTS THE CAPT'S AND FO'S ROLL CTLS FROM EACH OTHER GIVING ONLY 1/2 OF THE CTL TO EACH PLT. THE RPTR DOES NOT THINK THAT HE TURNED ON THE AUTOPLT INADVERTENTLY IN THIS INCIDENT; BUT THE EVIDENCE SEEMS TO SHOW OTHERWISE.