Narrative:

We were inbound to dtw in medium large transport X with the first officer flying at assigned altitude of 7000' at 250 KTS. I changed my radio transmitter to the other VHF radio to call the company that the flight was in range. During this procedure, I told the first officer I was off ATC frequency. He then knows that he would answer ATC while I talked to company. My audio was interphone (earphone, audio speaker off) so I could hear the company and not ATC. However, the first officer's overhead speaker was on. As I finished talking to my company, I heard 'our call sign...6000'.' I reached over and turned our altitude window/reminder from 7000 to 6000'. I saw the first officer pick up his microphone, but didn't hear his response because of the previously explained confign. I then completed the conversation with company and switched back to ATC radio confign. During that time, the first officer descended to 6000'. While level at 6000', ATC queried our altitude. I said we were at 6000'. He then informed me that the traffic he called out previously was at 6000'! But, by this time, the traffic had been well clear and he said to stay at 6000'. I apologized. What happened was the controller called out the traffic at 6000', I heard the altitude and thought I was setting the assigned altitude (over the first officer's cabin speaker). This obviously set the first officer in confusion as he answered to ATC concerning the traffic. But, he saw me (the captain) reach over and set 6000 from 7000'. Hey! The captain's always right, right? Whoa, wrong! Down he goes to 6000'. How many times does the right amount of circumstances occur when you are busy? This medium large transport type is the busiest cockpit in our fleet.

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Original NASA ASRS Text

Title: ACR LEFT ASSIGNED ALT, SETTING UP POTENTIAL CONFLICT WITH ANOTHER IFR ACFT. PLT DEVIATION.

Narrative: WE WERE INBND TO DTW IN MLG X WITH THE F/O FLYING AT ASSIGNED ALT OF 7000' AT 250 KTS. I CHANGED MY RADIO TRANSMITTER TO THE OTHER VHF RADIO TO CALL THE COMPANY THAT THE FLT WAS IN RANGE. DURING THIS PROC, I TOLD THE F/O I WAS OFF ATC FREQ. HE THEN KNOWS THAT HE WOULD ANSWER ATC WHILE I TALKED TO COMPANY. MY AUDIO WAS INTERPHONE (EARPHONE, AUDIO SPEAKER OFF) SO I COULD HEAR THE COMPANY AND NOT ATC. HOWEVER, THE F/O'S OVERHEAD SPEAKER WAS ON. AS I FINISHED TALKING TO MY COMPANY, I HEARD 'OUR CALL SIGN...6000'.' I REACHED OVER AND TURNED OUR ALT WINDOW/REMINDER FROM 7000 TO 6000'. I SAW THE F/O PICK UP HIS MIC, BUT DIDN'T HEAR HIS RESPONSE BECAUSE OF THE PREVIOUSLY EXPLAINED CONFIGN. I THEN COMPLETED THE CONVERSATION WITH COMPANY AND SWITCHED BACK TO ATC RADIO CONFIGN. DURING THAT TIME, THE F/O DSNDED TO 6000'. WHILE LEVEL AT 6000', ATC QUERIED OUR ALT. I SAID WE WERE AT 6000'. HE THEN INFORMED ME THAT THE TFC HE CALLED OUT PREVIOUSLY WAS AT 6000'! BUT, BY THIS TIME, THE TFC HAD BEEN WELL CLR AND HE SAID TO STAY AT 6000'. I APOLOGIZED. WHAT HAPPENED WAS THE CTLR CALLED OUT THE TFC AT 6000', I HEARD THE ALT AND THOUGHT I WAS SETTING THE ASSIGNED ALT (OVER THE F/O'S CABIN SPEAKER). THIS OBVIOUSLY SET THE F/O IN CONFUSION AS HE ANSWERED TO ATC CONCERNING THE TFC. BUT, HE SAW ME (THE CAPT) REACH OVER AND SET 6000 FROM 7000'. HEY! THE CAPT'S ALWAYS RIGHT, RIGHT? WHOA, WRONG! DOWN HE GOES TO 6000'. HOW MANY TIMES DOES THE RIGHT AMOUNT OF CIRCUMSTANCES OCCUR WHEN YOU ARE BUSY? THIS MLG TYPE IS THE BUSIEST COCKPIT IN OUR FLEET.

Data retrieved from NASA's ASRS site as of August 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.