Narrative:

During cruise flight, the captain had to leave the cockpit. I put on my mask (oxygen). The so (formerly a DC10 captain who down bid to so at age 60) got in the captain seat and motioned that I could take off my mask. I did so, believing that it was acceptable. Upon further checking of our manual, we later found that assumption to be incorrect. Although he had a type rating on the aircraft, it was not an adequate reason for me to remove my mask. The mask was in my hand ready for donning until the captain returned and was fully seated upon his return.

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Original NASA ASRS Text

Title: A DC10 FO DONNED HIS OXYGEN MASK WHEN THE CAPT LEFT THE FLT DECK. THE SO WAS AN AGED 60 RETIRED DC10 CAPT WHO HAD DOWN BID TO FE. THE SO TOOK THE CAPT'S SEAT IN ORDER TO RELIEVE THE FO FROM WEARING THE MASK. LATER, THEY FOUND OUT THAT THE SO WAS NO LONGER ALLOWED OR QUALIFIED TO SIT IN THE CAPT'S CHAIR.

Narrative: DURING CRUISE FLT, THE CAPT HAD TO LEAVE THE COCKPIT. I PUT ON MY MASK (OXYGEN). THE SO (FORMERLY A DC10 CAPT WHO DOWN BID TO SO AT AGE 60) GOT IN THE CAPT SEAT AND MOTIONED THAT I COULD TAKE OFF MY MASK. I DID SO, BELIEVING THAT IT WAS ACCEPTABLE. UPON FURTHER CHKING OF OUR MANUAL, WE LATER FOUND THAT ASSUMPTION TO BE INCORRECT. ALTHOUGH HE HAD A TYPE RATING ON THE ACFT, IT WAS NOT AN ADEQUATE REASON FOR ME TO REMOVE MY MASK. THE MASK WAS IN MY HAND READY FOR DONNING UNTIL THE CAPT RETURNED AND WAS FULLY SEATED UPON HIS RETURN.

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.