Narrative:

At the beginning of this flight the first officer tested his oxygen mask as prescribed and it tested perfectly. However, at 33000 ft when he pulled it out, as I was getting up to use the restroom, his mask was unusable. The bottom rear headhugger/airtube had stretched and blown out so the mask would not stay on his head by itself. We restowed the first officer's mask and tested it again in its holder as prescribed in the manual. It tested perfectly. This leads me to the conclusion that the first time any pilot really need to use this type of oxygen mask in an emergency situation is the first time that crew member would find out their oxygen mask is inoperative, if they had the same problem with their mask as we did with ours. I will check mine out of the holder and my first officer's each time.

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Original NASA ASRS Text

Title: A FK100 IN CRUISE AT FL330 HAD THE FO'S OXYGEN MASK FAIL WHEN ATTEMPTING TO DON THE MASK.

Narrative: AT THE BEGINNING OF THIS FLT THE FO TESTED HIS OXYGEN MASK AS PRESCRIBED AND IT TESTED PERFECTLY. HOWEVER, AT 33000 FT WHEN HE PULLED IT OUT, AS I WAS GETTING UP TO USE THE RESTROOM, HIS MASK WAS UNUSABLE. THE BOTTOM REAR HEADHUGGER/AIRTUBE HAD STRETCHED AND BLOWN OUT SO THE MASK WOULD NOT STAY ON HIS HEAD BY ITSELF. WE RESTOWED THE FO'S MASK AND TESTED IT AGAIN IN ITS HOLDER AS PRESCRIBED IN THE MANUAL. IT TESTED PERFECTLY. THIS LEADS ME TO THE CONCLUSION THAT THE FIRST TIME ANY PLT REALLY NEED TO USE THIS TYPE OF OXYGEN MASK IN AN EMER SIT IS THE FIRST TIME THAT CREW MEMBER WOULD FIND OUT THEIR OXYGEN MASK IS INOP, IF THEY HAD THE SAME PROB WITH THEIR MASK AS WE DID WITH OURS. I WILL CHK MINE OUT OF THE HOLDER AND MY FO'S EACH TIME.

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.