B737NG O2 system
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B737NG O2 system
Years ago, possibly B732 or B733, I was told, and read somewhere, that after use of the O2 mask it was necessary to turn off the O2 from the mask by closing the stowage left door and activating the test slide/button. I was also told that when the mask was out of the stowage the mic was automatically transferred from boom to mask, and it was necessary to perform the O2 off procedure to transfer the mic back to boom after usage.
Now I search the NG Vol 2 and can find no mention of this procedure. The O2 system looks the same as earlier models. Can anyone enlighten me with 100% facts?
Now I search the NG Vol 2 and can find no mention of this procedure. The O2 system looks the same as earlier models. Can anyone enlighten me with 100% facts?
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I think it depends on your audio control panel. Some have a selector switch "MASK - BOOM". Without this switch, the mic is automatically transferred due to a open/close switch on the mask stowage panel.
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I've looked at Vol 2 section 5. It is very brief and makes no mention of my scenario. On B732 there was the mask/boom switch. It did switch over the mic to mask, even with the mask stowed. However, I believed it was there primarily in case the auto switch-over function failed. The audio panel on B738 is very similar to the B732, as is most everything else regarding switches.
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OK; we are fixated on the mic; what about the O2? Surely it is necessary to secure the O2 flow from the mask and not deplete the bottle. Hence the closing of the left door and test switch activation. What about that as a necessity?
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When you do not turn the knob to EMERGENCY, the mask regulator supplies oxygen only when you inhale. There is no flow (except EMERGENCY) when you do not use the mask regardless the position of the left door.
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...however, if you keep the left door closed, not only will you not get any oxygen when you inhale, but also the harness will not inflate if you squeeze the handle. Since the left door directly operates the O2 shutoff valve within the mask box it prevents a leaky demand valve from slowly emptying the O2 bottle.
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Since the left door directly operates the O2 shutoff valve within the mask box it prevents a leaky demand valve from slowly emptying the O2 bottle.
That was my thinking: closing the left door when not in use was a belt & braces action. Has anyone else been taught this procedure?
That was my thinking: closing the left door when not in use was a belt & braces action. Has anyone else been taught this procedure?
