A FK100 in cruise at FL330 had the first officer's oxygen mask fail when attempting to don the mask.

Attributes
ACN	387194
Time
Date	199712
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : zbw
State Reference	MA
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute airway : zbw
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	387194
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

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.

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.