737NG Cabin Pressurization
The 737NG pressurization schedule is designed to meet FAR requirements as well as maximize cabin structure service life. The pressurization system uses a variable cabin pressure differential schedule based on airplane cruise altitude to meet these design requirements.
At cruise altitudes at or below FL 280, the max differential is 7.45 PSI. which will result in a cabin altitude of 8000’ at FL280. At cruise altitudes above FL280 but below FL370, the max differential is 7.80 PSI. which will result in a cabin altitude of 8000’ at FL370. At cruise altitudes above FL 370, the max differential is 8.35 PSI. which will result in a cabin altitude of 8000’ at FL410.
This functionality is different from other Boeing models which generally use a fixed max differential schedule thus can maintain lower cabin altitudes at cruise altitudes below the maximum certified altitude.
The above 3 paragraphs are from The Boeing 737 Technical Guide.
I have set my Flight Altitude to L350. I climb to L330 and maintain L330, without resetting my cruise altitude. How does this help the life cycle of an airframe?
After a while I rest my my Flight Altitude to L330. Now the cabin starts to descent why?
How does variable differential schedule differ from the fixed one?