Simviation Forum - Hypoxia at night

Reply #15 - Jan 13^th, 2010 at 1:32am

Splinter562 Offline
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You should check out the Pilot's Handbook of Aeronautical Knowledge, Chapter 16: Aeromedical Factors

http://www.faa.gov/library/manuals/aviation/pilot_handbook/

The last part of the chapter deals with night vision nicely.

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Reply #16 - Jan 13^th, 2010 at 6:25pm

beaky Offline
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SubZer0 wrote on Jan 12^th, 2010 at 10:21pm:

C, that is very interesting. My teacher now wants to know WHY are eyes more susceptible to the effects of hypoxia at night. Huh

Again:

http://www.aoa.org/x5352.xml

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Reply #17 - Jan 13^th, 2010 at 6:28pm

beaky Offline
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C wrote on Jan 12^th, 2010 at 1:27pm:

DaveSims wrote on Jan 12^th, 2010 at 1:00pm:

There is some basis for this, although it is not every night if my memory serves right (been 8 years since that class). I can not remember the exact reason, but hypoxia can occur at lower altitudes at night. We were usually advised to avoid flight above 8000MSL at night at our 141 school for just such reason.

I suspect its to do with diurnal (the recurring cycle between day and night for those unfamiliar) variation of the depth of the atmosphere of some sort.

*I may well be wrong!

I think the effects of diurnal variation, including nighttime temp. inversions, are pretty negligible as a risk factor for hypoxia at unusually low altitudes. I, too, could be wrong... but I doubt it. Grin

The big concern (and rightly so) about night flight is the pronounced effect that decreasing pressure has on night vision.

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Reply #18 - Jan 14^th, 2010 at 12:26am

SubZer0 Offline
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Thank you guys for the interest Wink

The answer is as follows:

During the night, the eyes use rods much more than cones. These rods are 10,000 times more sensitive than cones and therefore much more susceptible to hypoxia.

It's definitely in here, where Splinter said to look. Just read the entire section about night vision -- it's very interesting.

http://www.faa.gov/library/manuals/aviation/pilot_handbook/

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Reply #19 - Jan 14^th, 2010 at 3:24am

Mitch. Offline
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Some great information here. I trust we all learnt something, I know I have. Very helpful guys. Cool

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Reply #20 - Jan 14^th, 2010 at 6:19am

C Offline
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beaky wrote on Jan 13^th, 2010 at 6:28pm:

C wrote on Jan 12^th, 2010 at 1:27pm:

DaveSims wrote on Jan 12^th, 2010 at 1:00pm:

There is some basis for this, although it is not every night if my memory serves right (been 8 years since that class). I can not remember the exact reason, but hypoxia can occur at lower altitudes at night. We were usually advised to avoid flight above 8000MSL at night at our 141 school for just such reason.

I suspect its to do with diurnal (the recurring cycle between day and night for those unfamiliar) variation of the depth of the atmosphere of some sort.

*I may well be wrong!

I think the effects of diurnal variation, including nighttime temp. inversions, are pretty negligible as a risk factor for hypoxia at unusually low altitudes. I, too, could be wrong... but I doubt it. Grin

Quite! As I say, not something we really come across over here. Just thinking outside the box.

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