COURSE DEV -- NAV RECEIVER FAILURE AND NAV RECEIVER MISOP DESIGN PROB.

Narrative

BEFORE DEP #1 NAV RADIO WAS SET ON THE DCA VOR 328 RADIAL. THE #2 NAV RADIO WAS SET ON THE SMYRNA VOR 091 RADIAL. THE #2 VOR FLAG WAS DISPLAYED DURING TKOF BUT SHOULD HAVE DISAPPEARED AFTER TKOF. THE #1 NAV WAS CHANGED TO SMYRNA VOR AFTER WE WERE CLRED DIRECT EARLY IN THE CLB. THE PROB OCCURRED WHEN THE CAPT CHANGED #1 NAV FREQ AND UNKNOWINGLY AND INADVERTENTLY BUMPED THE VOLUME KNOB (WHICH IS ALSO AN OFF SWITCH) AND TURNED THE RECEIVER OFF. THE #2 NAV WAS OFF FROM THE BLOCKS WITH THE FLAG DISPLAYED; BUT WAS INTERPRETED AS AN INDICATION OF THE SMYRNA VOR OUT OF RANGE. THE NEXT RESULT OF THE ABOVE SIT WAS THAT 2 NAV RECEIVER FLAGS WERE DISPLAYED AND IT WAS ANALYZED AS RECEIVER FAILURES; AFTER THE ELECTRICAL SUPPLY WAS CHKED. ATC WAS ADVISED OF THE NAV PROB AND CLRNC WAS OBTAINED TO ENTER DOWNWIND AND LAND FROM VISUAL APCH TO RWY 36 AT DCA. THE QUESTION THAT NEEDS TO BE ASKED IS WHY THERE IS AN OFF SWITCH INCORPORATED INTO THE IDENTIFIER VOLUME KNOB. IN DISCUSSING THE OCCURRENCE WITH OTHER PLTS AND MECHS; THIS IS NOT THE FIRST TIME A CREW HAS BEEN 'TRAPPED' BY THIS SCENARIO; AND FURTHERMORE NONE WAS ABLE TO DETERMINE WHY THERE IS A NECESSITY FOR AN OFF SWITCH TO BE INCORPORATED IN THIS MANNER. THE GOOD NEWS IS THAT THE WORD IS OUT AND HOPEFULLY THIS EVENT WILL NOT OCCUR AGAIN IN THE NEAR FUTURE; ALTHOUGH I AM SURE IT WILL RECUR AS THE 'NEWNESS' OF THE INFO WEARS OFF AND SOMEONE ELSE WILL BE CAUGHT.