Narrative:

We were cleared by ZDC from FL210 to 11000' to be out of FL190 within the next 10 mi. We were deviating to the east of course because of a line of thunderstorms. The center controller was having a bad night; he was very busy and the standard response to his vectors was 'unable due to WX.' it didn't sound like he could see the WX on his scope. During our descent the F/a call light came on. I signalled the captain that I would be off the ATC communication radio to answer the call on the interphone. While I was speaking to the F/a's on interphone, captain asked me to stop because the bleed over from the interphone on his audio panel was making it impossible for him to hear the radio. I switched back to the ATC communication radio and acknowledged a clearance direct to gso. Passing 11500' center told us to maintain 12000'. I acknowledged that we were out of 11500' climbing back to 12000'. Center gave us an immediate left turn to 180 degrees and descended other traffic to 6000'. The moral of the story: when we preflight our O2 system before flight, many pilots leave the boom-mask switch on the audio selector panel in the 'mask' position (in an emergency when you have to don your O2 mask, you can communication west/O changing any switches). However, in our aircraft, when 'mask' is selected the interphone audio is automatically connected to your headset. In our situation, flying in this switch position prevented the captain from hearing a change in descent clearance from 11000 to 12000'. Also, because of his workload and the WX, ZDC missed the fact that we didn't receive or read back our amended clearance. I now fly with the boom-mask switch in the 'boom' position and only switch to mask after donning my O2 mask

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Original NASA ASRS Text

Title: ACR MLG OVERSHOOTS ALT IN DESCENT.

Narrative: WE WERE CLRED BY ZDC FROM FL210 TO 11000' TO BE OUT OF FL190 WITHIN THE NEXT 10 MI. WE WERE DEVIATING TO THE E OF COURSE BECAUSE OF A LINE OF TSTMS. THE CENTER CTLR WAS HAVING A BAD NIGHT; HE WAS VERY BUSY AND THE STANDARD RESPONSE TO HIS VECTORS WAS 'UNABLE DUE TO WX.' IT DIDN'T SOUND LIKE HE COULD SEE THE WX ON HIS SCOPE. DURING OUR DSNT THE F/A CALL LIGHT CAME ON. I SIGNALLED THE CAPT THAT I WOULD BE OFF THE ATC COM RADIO TO ANSWER THE CALL ON THE INTERPHONE. WHILE I WAS SPEAKING TO THE F/A'S ON INTERPHONE, CAPT ASKED ME TO STOP BECAUSE THE BLEED OVER FROM THE INTERPHONE ON HIS AUDIO PANEL WAS MAKING IT IMPOSSIBLE FOR HIM TO HEAR THE RADIO. I SWITCHED BACK TO THE ATC COM RADIO AND ACKNOWLEDGED A CLRNC DIRECT TO GSO. PASSING 11500' CENTER TOLD US TO MAINTAIN 12000'. I ACKNOWLEDGED THAT WE WERE OUT OF 11500' CLBING BACK TO 12000'. CENTER GAVE US AN IMMEDIATE LEFT TURN TO 180 DEGS AND DSNDED OTHER TFC TO 6000'. THE MORAL OF THE STORY: WHEN WE PREFLT OUR O2 SYS BEFORE FLT, MANY PLTS LEAVE THE BOOM-MASK SWITCH ON THE AUDIO SELECTOR PANEL IN THE 'MASK' POS (IN AN EMER WHEN YOU HAVE TO DON YOUR O2 MASK, YOU CAN COM W/O CHANGING ANY SWITCHES). HOWEVER, IN OUR ACFT, WHEN 'MASK' IS SELECTED THE INTERPHONE AUDIO IS AUTOMATICALLY CONNECTED TO YOUR HEADSET. IN OUR SITUATION, FLYING IN THIS SWITCH POS PREVENTED THE CAPT FROM HEARING A CHANGE IN DSNT CLRNC FROM 11000 TO 12000'. ALSO, BECAUSE OF HIS WORKLOAD AND THE WX, ZDC MISSED THE FACT THAT WE DIDN'T RECEIVE OR READ BACK OUR AMENDED CLRNC. I NOW FLY WITH THE BOOM-MASK SWITCH IN THE 'BOOM' POS AND ONLY SWITCH TO MASK AFTER DONNING MY O2 MASK

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.