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Preflight testing of oxygen systems (MH O2D2 failures)

Oxygen failure related posts moved from here and from another recent thread

Crossed the Alps IFR on top today in FL150 enroute to Portoroz (on the way to Athens) … when climbing through FL100 in IMC i realized that the O2D2 did not work. My son’s side did work though …

Decided to let the airplane climb to 150, undercast was about FL120 started playing with it, changed batteries (although i knew they were new), … nothing, my side did not work. Saturation down to below 80.

Opened a can of oxygen that’s always in the pocket behind the copilot’s seat and took some breaths every minute. I knew it would last until i could start the descent into Slovenia.

Then, all of a sudden, it started working …

Mistake i made: The normal cannulas with the manual valve which i can connect directly are in the baggage compartment. With one of those i could have solved the problem.

Last Edited by Flyer59 at 11 Aug 22:07

Thanks for sharing, especially the “lesson learned” part. Glad to know everything ended fine, and kudos for being prepared (canned oxygen).

EPKP - Kraków, Poland

Canned O2 will last how many minutes?

Shoreham EGKA, United Kingdom

That’s one of the reasons why i don’t like FL200, and above. Too many oxygen related dangers. FL150 i could fly for quite some time without O2, and if it had not worked again i would diverted a bit to the east where FL120 is possible IFR. I always have 2 of these cans at hand, and if i’m conservative it will last 15 minutes, but a shot every now and then feels good, and from FL150 i can descend to 130-120 in no time. I have no problems at FL120

One has to test the oxygen system before calling up an ATC unit which might give you a climb into an oxygen altitude.

If one has not done it on the ground, the best time to do it is on the handover to the first such controller. Before calling them up, is the best time to do stuff like that, or having a pee, or doing an MH370…

Shoreham EGKA, United Kingdom

Peter wrote:

One has to test the oxygen system before calling up an ATC unit which might give you a climb into an oxygen altitude.

Oxygen should be tested before engine start because you have to check for leaks which is hardly possible when engine is running.

LDZA LDVA, Croatia

That’s a good idea, Emir (hvala ;-)). Learn something new every day.

It was really completely stupid, although i did put new batteries into the O2D2 – and had a spare set in the cabin (although that was not the reason).

Flyer59 wrote:

it doesn’t work at 10.000 feet. If it had not worked at FL130

@Flyer59 – what exactly happened with the O2D2? Sorry, if I read it over. I’ve heard of some failures recently.


It was strange … the unit is almost new, was used five times before.

I had put in new batteries and had tested for the self test (sound) in the ground. I put it on “D10” and as it should it started at 10 k ft, but only the copilot side worked correctly. The red light on my side was flashing every now and then, but no oxygen.

Changed the batteries in the climb, no change. Checked all hoses and connections, nothing. Only after i pulled out my hose and put it in again it suddenly started working.

For the next high flight i’ll put the normal cannulas in the cabin which i can connect to the bottle regulator directly …

Mountain High have had problems recently with (they said) the firmware on the CPU getting corrupted. I have this in email from several pilots.

My two O2D2 units (four outlets total) have been faultless and the system does get used on almost every long flight I do. But they were bought several years ago.

Shoreham EGKA, United Kingdom
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