Narrative:

I was flying with a gentleman who is presently flying as a third officer. He is 60 and just retired as a captain and he has 20000+ hours of flight time. We were level at 23000' and were using rebreathing masks. He noted that he was starting to have symptoms of hypoxia, and became concerned that his O2 mask was not working correctly. I turned to check the connection of the mask (the connection is on the ceiling of the aircraft and also to see that the line was not kinked. All seemed in order, but he continued to have problems, so I found a nasal cannula in back and attached to a second outlet to give him 2 sources of O2. In the process of doing this, the aircraft climbed 700' (we were using the autoplt at the time). When I noticed the deviation from altitude, I started to correct and just as I did so ATC told me of the deviation. I stated that I had, 'just caught it.' at the time of the incident my 'copilot' was doing the communication to ATC, and with me, about such things as avoiding WX, using radar, etc. I wanted to pick his 20000 hour brain. Also earlier, when I first put on my mask, I used one that had a small rectangular flap (not a hole) cue in the side to allow my boom microphone to pass into the bask. ATC said the communication was garbled, so my copilot did the communication. Plus, his phraseology was more professional than mine. He did not have a microphone in his mask either (nor a flap cut in the side); he would lift the mask and use a hand microphone. On return flight things went uneventfully until I had been at 23000' for some time (I would guess 8-10 mins) when I noted the sudden onset of symptoms of hypoxia. I then attempted to check the source of O2 flow again, etc. I say, 'etc,' because things were really fuzzy for 2-3 mins. During this time, I apparently deviated from altitude (I was again using the autoplt). As the symptoms of hypoxia cleared (I had clasped the mask closely to my face and breathed furiously--not just deeply!), I became oriented enough again to comply with ATC's directions. Further on I asked to descend and to continue on VFR, as I had passed over the clouds. I did this and the rest of the flight was uneventful. After much reflection (it seems ridiculously simple now), the problem both times was not with the O2 system, or with the masks, or with any kinks in the O2 lines, but with the fact that my copilot and I both removed the masks from our faces to communication with ATC. This made the masks much less effective, and the result was hypoxia. I have 2 masks with mics in them (neither were in the aircraft at the time). One is very bulky and requires that I tape the top of the mask to my nose so my glasses won't fog up, and the other one (which I had purchased just within the past month to try and get around the problem of the bulkiness of the mask that came with the aircraft) will, on occasion, cause a squeal to be heard in the headphones. Thus, I had tried to devise the system of cutting a flap in the side of the mask and passing the boom microphone through. In order to avoid this situation ever occurring again, I am doing the following: 1) I now have rolls of tape and defogging spray in the aircraft to use with the bulky (but very safe) mask with the microphone installed, and I am having the second mask checked to see if the cause of the intermittent squeal can be found. 2) I am also flying today with my multi engine instrument with an ear oximeter from our local hospital on board to see if I can duplicate what happened and see how desaturated my hemoglobin becomes before symptoms of hypoxia start, and how long it stays desaturated before I become oriented again. I have not been able to find information of this sort, on the length of hypoxic-induced disorientation after an adequate O2 supply is reestablished, or the degree of desaturation to become disoriented. 3) we will also see if the autoplt will or will not hold altitude at 23000-26000', and if he thinks necessary, I will have the autoplt bench tested. 4) I am having an altitude alert device installed in the aircraft, because if the autoplt can deviate from altitude one time, it may do it again in a more critical situation. I am certainly embarrassed by this event. I try very hard to be a competent and quite conservative pilot, and I am taking measures to minimize the likelihood of this every being repeated. Obviously, when a mask is used it needs to be used correctly and not removed from the face to communicate with ATC or other passenger.

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Original NASA ASRS Text

Title: PLT AND OBSERVER IN SMT CRUISING AT FL230. OBSERVER EXPERIENCED HYPOXIA. ON RETURN FLT PLT EXPERIENCED HYPOXIA SYMPTOMS, BUT MANAGED TO SUCK IN ENOUGH O2 TO OVERCOME THE HYPOXIA.

Narrative: I WAS FLYING WITH A GENTLEMAN WHO IS PRESENTLY FLYING AS A THIRD OFFICER. HE IS 60 AND JUST RETIRED AS A CAPT AND HE HAS 20000+ HRS OF FLT TIME. WE WERE LEVEL AT 23000' AND WERE USING REBREATHING MASKS. HE NOTED THAT HE WAS STARTING TO HAVE SYMPTOMS OF HYPOXIA, AND BECAME CONCERNED THAT HIS O2 MASK WAS NOT WORKING CORRECTLY. I TURNED TO CHK THE CONNECTION OF THE MASK (THE CONNECTION IS ON THE CEILING OF THE ACFT AND ALSO TO SEE THAT THE LINE WAS NOT KINKED. ALL SEEMED IN ORDER, BUT HE CONTINUED TO HAVE PROBS, SO I FOUND A NASAL CANNULA IN BACK AND ATTACHED TO A SECOND OUTLET TO GIVE HIM 2 SOURCES OF O2. IN THE PROCESS OF DOING THIS, THE ACFT CLBED 700' (WE WERE USING THE AUTOPLT AT THE TIME). WHEN I NOTICED THE DEVIATION FROM ALT, I STARTED TO CORRECT AND JUST AS I DID SO ATC TOLD ME OF THE DEVIATION. I STATED THAT I HAD, 'JUST CAUGHT IT.' AT THE TIME OF THE INCIDENT MY 'COPLT' WAS DOING THE COM TO ATC, AND WITH ME, ABOUT SUCH THINGS AS AVOIDING WX, USING RADAR, ETC. I WANTED TO PICK HIS 20000 HR BRAIN. ALSO EARLIER, WHEN I FIRST PUT ON MY MASK, I USED ONE THAT HAD A SMALL RECTANGULAR FLAP (NOT A HOLE) CUE IN THE SIDE TO ALLOW MY BOOM MIC TO PASS INTO THE BASK. ATC SAID THE COM WAS GARBLED, SO MY COPLT DID THE COM. PLUS, HIS PHRASEOLOGY WAS MORE PROFESSIONAL THAN MINE. HE DID NOT HAVE A MIC IN HIS MASK EITHER (NOR A FLAP CUT IN THE SIDE); HE WOULD LIFT THE MASK AND USE A HAND MIC. ON RETURN FLT THINGS WENT UNEVENTFULLY UNTIL I HAD BEEN AT 23000' FOR SOME TIME (I WOULD GUESS 8-10 MINS) WHEN I NOTED THE SUDDEN ONSET OF SYMPTOMS OF HYPOXIA. I THEN ATTEMPTED TO CHK THE SOURCE OF O2 FLOW AGAIN, ETC. I SAY, 'ETC,' BECAUSE THINGS WERE REALLY FUZZY FOR 2-3 MINS. DURING THIS TIME, I APPARENTLY DEVIATED FROM ALT (I WAS AGAIN USING THE AUTOPLT). AS THE SYMPTOMS OF HYPOXIA CLRED (I HAD CLASPED THE MASK CLOSELY TO MY FACE AND BREATHED FURIOUSLY--NOT JUST DEEPLY!), I BECAME ORIENTED ENOUGH AGAIN TO COMPLY WITH ATC'S DIRECTIONS. FURTHER ON I ASKED TO DSND AND TO CONTINUE ON VFR, AS I HAD PASSED OVER THE CLOUDS. I DID THIS AND THE REST OF THE FLT WAS UNEVENTFUL. AFTER MUCH REFLECTION (IT SEEMS RIDICULOUSLY SIMPLE NOW), THE PROB BOTH TIMES WAS NOT WITH THE O2 SYS, OR WITH THE MASKS, OR WITH ANY KINKS IN THE O2 LINES, BUT WITH THE FACT THAT MY COPLT AND I BOTH REMOVED THE MASKS FROM OUR FACES TO COM WITH ATC. THIS MADE THE MASKS MUCH LESS EFFECTIVE, AND THE RESULT WAS HYPOXIA. I HAVE 2 MASKS WITH MICS IN THEM (NEITHER WERE IN THE ACFT AT THE TIME). ONE IS VERY BULKY AND REQUIRES THAT I TAPE THE TOP OF THE MASK TO MY NOSE SO MY GLASSES WON'T FOG UP, AND THE OTHER ONE (WHICH I HAD PURCHASED JUST WITHIN THE PAST MONTH TO TRY AND GET AROUND THE PROB OF THE BULKINESS OF THE MASK THAT CAME WITH THE ACFT) WILL, ON OCCASION, CAUSE A SQUEAL TO BE HEARD IN THE HEADPHONES. THUS, I HAD TRIED TO DEVISE THE SYS OF CUTTING A FLAP IN THE SIDE OF THE MASK AND PASSING THE BOOM MIC THROUGH. IN ORDER TO AVOID THIS SITUATION EVER OCCURRING AGAIN, I AM DOING THE FOLLOWING: 1) I NOW HAVE ROLLS OF TAPE AND DEFOGGING SPRAY IN THE ACFT TO USE WITH THE BULKY (BUT VERY SAFE) MASK WITH THE MIC INSTALLED, AND I AM HAVING THE SECOND MASK CHKED TO SEE IF THE CAUSE OF THE INTERMITTENT SQUEAL CAN BE FOUND. 2) I AM ALSO FLYING TODAY WITH MY MULTI ENG INSTR WITH AN EAR OXIMETER FROM OUR LCL HOSPITAL ON BOARD TO SEE IF I CAN DUPLICATE WHAT HAPPENED AND SEE HOW DESATURATED MY HEMOGLOBIN BECOMES BEFORE SYMPTOMS OF HYPOXIA START, AND HOW LONG IT STAYS DESATURATED BEFORE I BECOME ORIENTED AGAIN. I HAVE NOT BEEN ABLE TO FIND INFO OF THIS SORT, ON THE LENGTH OF HYPOXIC-INDUCED DISORIENTATION AFTER AN ADEQUATE O2 SUPPLY IS REESTABLISHED, OR THE DEGREE OF DESATURATION TO BECOME DISORIENTED. 3) WE WILL ALSO SEE IF THE AUTOPLT WILL OR WILL NOT HOLD ALT AT 23000-26000', AND IF HE THINKS NECESSARY, I WILL HAVE THE AUTOPLT BENCH TESTED. 4) I AM HAVING AN ALT ALERT DEVICE INSTALLED IN THE ACFT, BECAUSE IF THE AUTOPLT CAN DEVIATE FROM ALT ONE TIME, IT MAY DO IT AGAIN IN A MORE CRITICAL SITUATION. I AM CERTAINLY EMBARRASSED BY THIS EVENT. I TRY VERY HARD TO BE A COMPETENT AND QUITE CONSERVATIVE PLT, AND I AM TAKING MEASURES TO MINIMIZE THE LIKELIHOOD OF THIS EVERY BEING REPEATED. OBVIOUSLY, WHEN A MASK IS USED IT NEEDS TO BE USED CORRECTLY AND NOT REMOVED FROM THE FACE TO COMMUNICATE WITH ATC OR OTHER PAX.

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.