737Jock
What would you do if there weren't any papi's?
As 737Jock wrote,what would you do?
The PAPIS are only one of the available visual aids to maintain a steady profile to touchdown,the angle can vary as long as you maintain stabilised criteria such as rate of descent,touchdown point (within touchdown zone and within the landing diatance you calculated to be a safe touch down distance for the runway lengh and conditions.
I remember my first lesson on papis:
"4 whites:wake up!,4 reds youre about dead!"
In between,it varies with calibration of the papis,some are design for high flight deck such as 747 and a B 737 will see 3 reds 1 white to maintain 3 deg and 1000 feet touchdown aiming point..
So 4 whites is a reference,a visual aid and not a factor for systematically having to go around,but remember,the closer you get in,the least margin you have,so it may be prudent to go around if by 500 ft you are not where you wish or recommended to be in your profile.