AiF uses an armor save. The save doesn't block 100% of the damage but only a portion of the damage based on the type of armor (1/3 for leather 1/2 for chain and 2/3s for plate). To see how this compares to all-or-nothing save, I converted the AiF numbers to a straight save percentage. For example, in AiF plate armor blocks 2/3s of the damage 90% of the time which works out to blocking all damage 60% of the time (keeping the same average per round).

Leather: 18.3%
Chainmail: 30%
Full Plate: 60%

A few years ago, I calculated the save percentages from OD&D's alternate combat system by looking at the hits deflected by a higher AC. (how many AC9 "hits" are converted to "misses" based on a higher AC). Those numbers were:

Leather (AC7): 18%
Chainmail: 35%
Plate: 55%

As you can see, both sets of numbers are within 5% of each other. That surprised me.

Converting the AiF numbers to a d20 roll-high save gives the saves as:

Leather: 17+
Chain: 15+
Plate: 9+

Converted to a simple d6 roll:

Leather: 6
Chain: 5-6
Plate: 4-6

I'm not sure what to do about helmets. The AiF rule gives helmets a 10% save but it's not clear if that is rolled separately, if it is added to the other percentage, or if that roll is for having a helmet only and helmets are assumed into part of the other suits.

What a good contribution to the discussion!
That calculation surprises me as well.

:shock: The similarity between the two sets of numbers caught me off guard! :shock:

Seriously, this is worth taking note of and pursuing.

Interesting!

How do you feel about turning the AiF system into an all or nothing save?

-Havard