Narrative:

Aircraft is one of several -900's and a few late model -800's (those delivered around the same time as the first -900's) that I have flown that have a different setup in regards to the audio system. The problem is that all aural alerts, such as altitude chime, radar altimeter callouts, TCAS advisories, windshear alerts, etc, are broadcast directly into the pilot's headsets, as well as over the speakers (like the rest of the fleet). I have not found a way to turn down the volume of the alert in my headset. It is not controled by the communication volume knobs. I have, in the past, had ATC attempt to tell me of a potential traffic conflict, just as TCAS drowns out the controller yelling 'traffic!! Traffic!!' in my ear. Even the altitude alert chime can make it very difficult to hear what is being said over the radio. I can see a controller telling the crew to go around while the RA is counting down the altitude on a very short final. It is possible that a crew in that situation will not hear the controller's instructions and complete their landing. I feel this is a safety hazard that should be addressed. Callback conversation with reporter revealed the following information: the reporter stated the audio control panel has no control over the aural alerts, TCAS RA, GPWS, altitude chimes, and radar altimeter callouts. The reporter said previous experiences with ATC advising of potential conflict is drowned out with high volume aural alerts in headset and speakers such as, 'traffic!! Traffic!!' the reporter stated another situation has the controller telling the crew to go around with the radio altimeter counting down the altitude on short final. The reporter said the newer airplanes B737-900 and later B737-800 are in this configuration. The problem now exists that some of these units are being swapped around throughout the B737-900 and B737-800 fleets.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B737-900 AND 800 FIRST OFFICER RPTS HIGH VOLUME AURAL ALERTS, GPWS, AND TCAS RA OVERRIDE NORMAL COM AUDIO. UNABLE TO CTL SOUND VOLUME OF ALERTS.

Narrative: ACFT IS ONE OF SEVERAL -900'S AND A FEW LATE MODEL -800'S (THOSE DELIVERED AROUND THE SAME TIME AS THE FIRST -900'S) THAT I HAVE FLOWN THAT HAVE A DIFFERENT SETUP IN REGARDS TO THE AUDIO SYSTEM. THE PROB IS THAT ALL AURAL ALERTS, SUCH AS ALT CHIME, RADAR ALTIMETER CALLOUTS, TCAS ADVISORIES, WINDSHEAR ALERTS, ETC, ARE BROADCAST DIRECTLY INTO THE PLT'S HEADSETS, AS WELL AS OVER THE SPEAKERS (LIKE THE REST OF THE FLEET). I HAVE NOT FOUND A WAY TO TURN DOWN THE VOLUME OF THE ALERT IN MY HEADSET. IT IS NOT CTLED BY THE COM VOLUME KNOBS. I HAVE, IN THE PAST, HAD ATC ATTEMPT TO TELL ME OF A POTENTIAL TFC CONFLICT, JUST AS TCAS DROWNS OUT THE CTLR YELLING 'TFC!! TFC!!' IN MY EAR. EVEN THE ALT ALERT CHIME CAN MAKE IT VERY DIFFICULT TO HEAR WHAT IS BEING SAID OVER THE RADIO. I CAN SEE A CTLR TELLING THE CREW TO GAR WHILE THE RA IS COUNTING DOWN THE ALT ON A VERY SHORT FINAL. IT IS POSSIBLE THAT A CREW IN THAT SIT WILL NOT HEAR THE CTLR'S INSTRUCTIONS AND COMPLETE THEIR LNDG. I FEEL THIS IS A SAFETY HAZARD THAT SHOULD BE ADDRESSED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AUDIO CTL PANEL HAS NO CONTROL OVER THE AURAL ALERTS, TCAS RA, GPWS, ALT CHIMES, AND RADAR ALTIMETER CALLOUTS. THE RPTR SAID PREVIOUS EXPERIENCES WITH ATC ADVISING OF POTENTIAL CONFLICT IS DROWNED OUT WITH HIGH VOLUME AURAL ALERTS IN HEADSET AND SPEAKERS SUCH AS, 'TFC!! TFC!!' THE RPTR STATED ANOTHER SIT HAS THE CTLR TELLING THE CREW TO GAR WITH THE RADIO ALTIMETER COUNTING DOWN THE ALT ON SHORT FINAL. THE RPTR SAID THE NEWER AIRPLANES B737-900 AND LATER B737-800 ARE IN THIS CONFIGURATION. THE PROB NOW EXISTS THAT SOME OF THESE UNITS ARE BEING SWAPPED AROUND THROUGHOUT THE B737-900 AND B737-800 FLEETS.

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.