Narrative:

While being vectored for the ILS approach to runway 26R, we were given a heading of 180 degrees. After a moment, I looked to my right and noticed we were about to go past the extended centerline of the runway. We tried calling approach but heard no response. After about 30 seconds, we realized that we accidentally turned the volume down on the radio control head. (The older control head on this particular aircraft needs to be replaced.) after re-establishing radio contact, we continued the approach. Supplemental information from acn 477523: we were on a radar vector 9205 degrees, I think) 6000 ft and 210 KIAS assigned. Radios worked fine until somewhere on approach with atl. After a short time (5 mins?) we saw atl itself about 15 mi or so, 2 O'clock position. Commented that the controller must be out to lunch, and started calling him. We called 2-3 times with no luck. I turned radio all the way up and could barely hear any radio traffic. We switched to communication #2 radio, still no luck. Back to communication #1 again. Again, I turned radio up all the way and suddenly volume came on full volume. Approach advised us they had called us many times. We asked if they'd heard our call. They said 'no.' the best guess I can give as to what happened is this: there are some B737-200's that are radically different than our standard B737-200's. The knob design is such that while changing frequencys, you can easily turn the volume knob either up or down, depending on which direction you turn the frequency knobs. I, or the captain, may have turned the volume knob all the way down with a frequency change. When the volume is all the way 'quiet,' it is also in a detented position (I just learned this). The volume knob normally turns easily. However, if in this detent, the knob doesn't easily turn. When I first began attempting contact, I felt the knob -- it felt as if it were on the full loud stop when in reality it was in the full quiet detent. The 2 main points I can boil this narrative down to are: 1) the design of the volume/frequency knob is poor and is easily turned all the way down when changing a frequency. 2) volume knob in 'full quiet' position is in a detent. When you are in the detent, it's easy to confuse this with 'maximum volume.' most people don't turn these knobs hard or you'll blow your (and your crew mate's) ears out. Using the normal soft touch, is easy to confuse with maximum volume.

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Original NASA ASRS Text

Title: B737 CREW LOST COM WITH ATL APCH CTL.

Narrative: WHILE BEING VECTORED FOR THE ILS APCH TO RWY 26R, WE WERE GIVEN A HDG OF 180 DEGS. AFTER A MOMENT, I LOOKED TO MY R AND NOTICED WE WERE ABOUT TO GO PAST THE EXTENDED CTRLINE OF THE RWY. WE TRIED CALLING APCH BUT HEARD NO RESPONSE. AFTER ABOUT 30 SECONDS, WE REALIZED THAT WE ACCIDENTALLY TURNED THE VOLUME DOWN ON THE RADIO CTL HEAD. (THE OLDER CTL HEAD ON THIS PARTICULAR ACFT NEEDS TO BE REPLACED.) AFTER RE-ESTABLISHING RADIO CONTACT, WE CONTINUED THE APCH. SUPPLEMENTAL INFO FROM ACN 477523: WE WERE ON A RADAR VECTOR 9205 DEGS, I THINK) 6000 FT AND 210 KIAS ASSIGNED. RADIOS WORKED FINE UNTIL SOMEWHERE ON APCH WITH ATL. AFTER A SHORT TIME (5 MINS?) WE SAW ATL ITSELF ABOUT 15 MI OR SO, 2 O'CLOCK POS. COMMENTED THAT THE CTLR MUST BE OUT TO LUNCH, AND STARTED CALLING HIM. WE CALLED 2-3 TIMES WITH NO LUCK. I TURNED RADIO ALL THE WAY UP AND COULD BARELY HEAR ANY RADIO TFC. WE SWITCHED TO COM #2 RADIO, STILL NO LUCK. BACK TO COM #1 AGAIN. AGAIN, I TURNED RADIO UP ALL THE WAY AND SUDDENLY VOLUME CAME ON FULL VOLUME. APCH ADVISED US THEY HAD CALLED US MANY TIMES. WE ASKED IF THEY'D HEARD OUR CALL. THEY SAID 'NO.' THE BEST GUESS I CAN GIVE AS TO WHAT HAPPENED IS THIS: THERE ARE SOME B737-200'S THAT ARE RADICALLY DIFFERENT THAN OUR STANDARD B737-200'S. THE KNOB DESIGN IS SUCH THAT WHILE CHANGING FREQS, YOU CAN EASILY TURN THE VOLUME KNOB EITHER UP OR DOWN, DEPENDING ON WHICH DIRECTION YOU TURN THE FREQ KNOBS. I, OR THE CAPT, MAY HAVE TURNED THE VOLUME KNOB ALL THE WAY DOWN WITH A FREQ CHANGE. WHEN THE VOLUME IS ALL THE WAY 'QUIET,' IT IS ALSO IN A DETENTED POS (I JUST LEARNED THIS). THE VOLUME KNOB NORMALLY TURNS EASILY. HOWEVER, IF IN THIS DETENT, THE KNOB DOESN'T EASILY TURN. WHEN I FIRST BEGAN ATTEMPTING CONTACT, I FELT THE KNOB -- IT FELT AS IF IT WERE ON THE FULL LOUD STOP WHEN IN REALITY IT WAS IN THE FULL QUIET DETENT. THE 2 MAIN POINTS I CAN BOIL THIS NARRATIVE DOWN TO ARE: 1) THE DESIGN OF THE VOLUME/FREQ KNOB IS POOR AND IS EASILY TURNED ALL THE WAY DOWN WHEN CHANGING A FREQ. 2) VOLUME KNOB IN 'FULL QUIET' POS IS IN A DETENT. WHEN YOU ARE IN THE DETENT, IT'S EASY TO CONFUSE THIS WITH 'MAX VOLUME.' MOST PEOPLE DON'T TURN THESE KNOBS HARD OR YOU'LL BLOW YOUR (AND YOUR CREW MATE'S) EARS OUT. USING THE NORMAL SOFT TOUCH, IS EASY TO CONFUSE WITH MAX VOLUME.

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.