Very basic question from a student: GA pilots are urged to fly 5,000 or below at night, in order to preserve night vision. As many large transport jets can not pressurize to anywhere near 5,000, why do transport pilots get to fly at night? Is night vision less important in transport flying? Example: Boeing 767, 6,900' cabin pressure at 39,000'.

 

That is a good question.

Depending on the aircraft cruise alt cabins can be kept between 5-6k. 5k is a general guideline, hypoxia will affect people in many different ways.

(Opinion) Also night vision unfortunately isn't as stressed in airplanes heading for class A airspace. Many of these cockpits are designed with lots of white light too. Night vision is important but not as import as in a c152 around 1000 feet.

 

You aren't urged to stay at 5000' or below at night, just recommended to have oxygen for vision above those altitudes. "Urged" is a pretty strong word and black things at night are usually the earth at some ground level. Transport can pressurize to 5000', if it's within the max differential PSI for the altitude they are flying, but they may pressurize at a higher cabin alt if flying higher where the max differential does not allow. Also, a lot of GA pilots, probably more-so than airline pilots, may be smokers, not very fit, from sea level, etc. due to less regulation and they don't usually experience going up to 8000 PA like some airline pilots do every day. Lastly, transport category aircraft have much more redundancy, two pilots, following GS down on the approaches, always on airways or segments with minimum altitudes for terrain clearance, etc. Equipped with TAWS.

 

I grew up and learned to fly in a location where my house, let alone field elevation or any flight altitude, was above the FAA recommendation for oxygen at night. Were I to have adhered to that guideline, I'd have needed oxygen to go to bed at night, drive, or walk about town, let alone fly. That's a ridiculous notion.

Why do pilots in pressurized cockpits not utilize oxygen at cabin pressure altitudes of 5,000' or higher? Despite the FAA's extremely conservative recommendation, no regulatory requirement exists for oxygen at that altitude.

 

I would agree it depends on your personal physiology to a large degree. Altitude acclimation is a factor, and age, fitness, and smoking are big factors.

If you're doing the kind of flying where night vision could be critical (not most 121) then you might benefit from supplements, especially if you eat like crap.

 

The cabin altitude on most transport aircraft is only at that level in cruise. By the time night vision is a factor during approach the cabin has been below 5000 for at least 20 minutes and probably at field elevation for the actual approach.

 

Field elevation may be above 5,000'