B737-900 first officer complains of the audio panel design wherein the GPWS and altitude alert signa...

Attributes
ACN	622228
Time
Date	200304
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl bound upper : 50
Environment
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-900
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	622228
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : less severe non adherence other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	other
Supplementary
Problem Areas	Company Aircraft

Narrative:

Certain aircraft within the B737-900 fleet sound the altitude alerter/egpws system alerts through the audio panel, and thus the pilot's headset. I believe this to be a hazardous confign due to the possibility (and probability) of missing an important ATC instruction due to an altitude alert. At various points during these flts, ATC instructions were blocked by the altitude alerter's tone sounding at an inopportune moment. Luckily, it did not cause us to deviate from ATC instructions on these 2 particular flts. But, it has caused me to ask ATC to repeat their instructions to us, on previous flts -- one when we were about to intercept a localizer course to an airport with parallel runways. I am concerned by the possibility that a control tower could issue 'go around' instructions to an aircraft (perhaps due to a runway incursion), just when the egpws is counting down (100-50-30-20-10), and the flight crew's inability to hear those instructions due to the volume level of the alerts. I hope that this situation can be resolved as the -900 aircraft are cycled through maintenance.

Original NASA ASRS Text

Title: B737-900 FO COMPLAINS OF THE AUDIO PANEL DESIGN WHEREIN THE GPWS AND ALT ALERT SIGNALS ARE CHANNELED THROUGH THE PANEL TO THE CREW'S HEADSETS, THEREBY POSSIBLY CREATING A LOSS OF COM WITH ATC.

Narrative: CERTAIN ACFT WITHIN THE B737-900 FLEET SOUND THE ALT ALERTER/EGPWS SYS ALERTS THROUGH THE AUDIO PANEL, AND THUS THE PLT'S HEADSET. I BELIEVE THIS TO BE A HAZARDOUS CONFIGN DUE TO THE POSSIBILITY (AND PROBABILITY) OF MISSING AN IMPORTANT ATC INSTRUCTION DUE TO AN ALT ALERT. AT VARIOUS POINTS DURING THESE FLTS, ATC INSTRUCTIONS WERE BLOCKED BY THE ALT ALERTER'S TONE SOUNDING AT AN INOPPORTUNE MOMENT. LUCKILY, IT DID NOT CAUSE US TO DEVIATE FROM ATC INSTRUCTIONS ON THESE 2 PARTICULAR FLTS. BUT, IT HAS CAUSED ME TO ASK ATC TO REPEAT THEIR INSTRUCTIONS TO US, ON PREVIOUS FLTS -- ONE WHEN WE WERE ABOUT TO INTERCEPT A LOC COURSE TO AN ARPT WITH PARALLEL RWYS. I AM CONCERNED BY THE POSSIBILITY THAT A CTL TWR COULD ISSUE 'GO AROUND' INSTRUCTIONS TO AN ACFT (PERHAPS DUE TO A RWY INCURSION), JUST WHEN THE EGPWS IS COUNTING DOWN (100-50-30-20-10), AND THE FLT CREW'S INABILITY TO HEAR THOSE INSTRUCTIONS DUE TO THE VOLUME LEVEL OF THE ALERTS. I HOPE THAT THIS SIT CAN BE RESOLVED AS THE -900 ACFT ARE CYCLED THROUGH MAINT.

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.

B737-900 first officer complains of the audio panel design wherein the GPWS and altitude alert signals are channeled through the panel to the crew's headsets, thereby possibly creating a loss of communication with ATC.