Narrative:

First day of three day trip; second leg of first day. Flying with this first officer for first time. He wanted to use headsets and intercom mode with headsets. I don't usually use intercom and headsets at cruise; I use speakers.this time I thought I would honor his wish and try headsets. Worked well on first leg; I was flying and he was talking to ATC. Second leg I was talking to ATC and he was flying. Approximately 10 minutes after level off at FL380 and after PA to passengers we hooked up our headset to intercom and spoke through headsets.I inadvertently selected 'receiver/transmitter (right/T)' instead of 'intercom (I/C)' on radio tuning panel transmitting our conversation over active washington center frequency. It seemed like 5 to 7 minutes and I realized I wasn't hearing ATC or other aircraft. I immediately disconnected my intercom and called ATC. Washington center told us we had been transmitting our conversation for about 10 minutes and instructed us to call jacksonville center. I was shocked; embarrassed and humiliated all at the same time!this will never happen again as mistakes that embarrass and humiliate are very good learning lessons toward future actions! Have felt terrible about this for last several days as I understand the possible hazards for us and everyone else using this frequency during that time.I think the labeling on these radio intercom switches should have a better identifier saying something along the lines of 'external transmissions' and not just right/T!it was also at night and hard to see labeling on switch.if you are transmitting on B-777 for more than 20 or 30 seconds you get 'icas' message saying 'transmit!!' letting you know of potential stuck mic.

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Original NASA ASRS Text

Title: B737-800 Captain reported mistakenly transmitting personal conversation on ATC frequency when he set the radio panel up incorrectly.

Narrative: First day of three day trip; second leg of first day. Flying with this First Officer for first time. He wanted to use headsets and intercom mode with headsets. I don't usually use intercom and headsets at cruise; I use speakers.This time I thought I would honor his wish and try headsets. Worked well on first leg; I was flying and he was talking to ATC. Second leg I was talking to ATC and he was flying. Approximately 10 minutes after level off at FL380 and after PA to passengers we hooked up our headset to intercom and spoke through headsets.I inadvertently selected 'Receiver/Transmitter (R/T)' instead of 'Intercom (I/C)' on radio tuning panel transmitting our conversation over active Washington Center frequency. It seemed like 5 to 7 minutes and I realized I wasn't hearing ATC or other aircraft. I immediately disconnected my intercom and called ATC. Washington Center told us we had been transmitting our conversation for about 10 minutes and instructed us to call Jacksonville Center. I was shocked; embarrassed and humiliated all at the same time!This will never happen again as mistakes that embarrass and humiliate are very good learning lessons toward future actions! Have felt terrible about this for last several days as I understand the possible hazards for us and everyone else using this frequency during that time.I think the labeling on these radio intercom switches should have a better identifier saying something along the lines of 'external transmissions' and not just R/T!It was also at night and hard to see labeling on switch.If you are transmitting on B-777 for more than 20 or 30 seconds you get 'ICAS' message saying 'TRANSMIT!!' Letting you know of potential stuck mic.

Data retrieved from NASA's ASRS site 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.