3 bar VASI clarification
 

Hello People

I found two different explanations online for the 3 bar VASI and I'm hoping somebody can clarify how they really work.

1st explanation is: if you got Red Red Red of course you are low.
WRR on Lower Glide path
WWR on Upper Glide path
WWW obviously High

If this is correct how do I know if I should maintain the Lower or Upper glide?

2nd explanation goes: You only get to use two out of the three bars, if you are flying a High Cockpit aircraft you disregard the lower bar and you should get 1 R and 1 W to be on the glide.
If you are flying a Low Cockpit aircraft you disregard the top bar.

But if this is the case, what's the definition of a High Cockpit aircraft? does it mean a Wide Body aircraft?

Guys, any information about the 3 bar VASI will be appreciated

High Cockpit means an aircraft that in landing attitude, positions the cockpit 25 feet (8 meters) or more above the extended landing gear.

Most wide-bodies will qualify.

A few oddball narrow-bodies might also qualify, however.

https://i.pinimg.com/originals/da/bc...3d306e07f9.jpg

Technically, the FAA assigns four "Height Groups," to cover planes from small GA/bizjet (cockpit height less than 10 feet above gear) up to 747s, An-124s, C-5s, etc. Group 4 is the high-cockpit group.

The upper glide path of the 3-bar VASI ensures a cockpit (pilot eye-point) threshold crossing height of 75 feet. The lower 3-bar VASI glide path ensures a cockpit (eye-point) threshold crossing height of 40-50 feet.

pattern is full, thanks mate

Things are much clearer to me now, really appreciate your reply specially the threshold crossing heights.