Narrative:

The communication used on the aircraft have 2 frequency selection windows permitting the desired frequency to be selected first, and then activated by use of a transfer switch. (This allows you to retain the previous frequency until communications have been established on the new frequency.) after much use the habit pattern established is to select the newly assigned frequency, acknowledge the new frequency and immediately use the transfer switch. When the event in question happened the first officer was flying the aircraft while I was operating the radios. We were downwind, being vectored on a northerly heading for an ILS approach. Flight conditions were IFR. I preselected the frequency of the control tower, knowing that it would be the next frequency assigned by approach control. The habit pattern mentioned in the prologue took over and I hit the transfer switch. This put us on tower frequency before approach control had transferred us, and most important before they gave us a turn to base leg. Our northerly heading was taking us toward high terrain. We were now in the right pew, but had moved to the wrong church. At about the same time that we realized that the turn to base leg was overdue, the control tower contacted us and relayed a turn to final from a very worried, but alert, approach controller. I, for one, will not try to outguess or outsmart the system in the future, and hopefully not make a tough job even tougher.

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Original NASA ASRS Text

Title: ACR MLG FREQ CHANGE PREMATURE RESULTING IN CONTROLLED FLT TOWARD TERRAIN.

Narrative: THE COM USED ON THE ACFT HAVE 2 FREQ SELECTION WINDOWS PERMITTING THE DESIRED FREQ TO BE SELECTED FIRST, AND THEN ACTIVATED BY USE OF A TRANSFER SWITCH. (THIS ALLOWS YOU TO RETAIN THE PREVIOUS FREQ UNTIL COMS HAVE BEEN ESTABLISHED ON THE NEW FREQ.) AFTER MUCH USE THE HABIT PATTERN ESTABLISHED IS TO SELECT THE NEWLY ASSIGNED FREQ, ACKNOWLEDGE THE NEW FREQ AND IMMEDIATELY USE THE TRANSFER SWITCH. WHEN THE EVENT IN QUESTION HAPPENED THE F/O WAS FLYING THE ACFT WHILE I WAS OPERATING THE RADIOS. WE WERE DOWNWIND, BEING VECTORED ON A NORTHERLY HDG FOR AN ILS APCH. FLT CONDITIONS WERE IFR. I PRESELECTED THE FREQ OF THE CTL TWR, KNOWING THAT IT WOULD BE THE NEXT FREQ ASSIGNED BY APCH CTL. THE HABIT PATTERN MENTIONED IN THE PROLOGUE TOOK OVER AND I HIT THE TRANSFER SWITCH. THIS PUT US ON TWR FREQ BEFORE APCH CTL HAD TRANSFERRED US, AND MOST IMPORTANT BEFORE THEY GAVE US A TURN TO BASE LEG. OUR NORTHERLY HDG WAS TAKING US TOWARD HIGH TERRAIN. WE WERE NOW IN THE RIGHT PEW, BUT HAD MOVED TO THE WRONG CHURCH. AT ABOUT THE SAME TIME THAT WE REALIZED THAT THE TURN TO BASE LEG WAS OVERDUE, THE CTL TWR CONTACTED US AND RELAYED A TURN TO FINAL FROM A VERY WORRIED, BUT ALERT, APCH CTLR. I, FOR ONE, WILL NOT TRY TO OUTGUESS OR OUTSMART THE SYS IN THE FUTURE, AND HOPEFULLY NOT MAKE A TOUGH JOB EVEN TOUGHER.

Data retrieved from NASA's ASRS site as of August 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.