Originally Posted by SmilingBoy

Let me try (no guarantees!). It is mostly the same as UA. Differences in bold.

A = Discounted Fare First Class. Round The World First is booked in this class.
B = Almost Full Fare Economy with minimal restrictions
C = Full Fare Unrestricted Business Class
D = Discounted Fare Business - used also on all Business Class *A RTW fares
E = Lowest Economy fare domestic/intra-European. Changeable against a fee, though
F = Full Fare Unrestricted First Class
G = Economy fare, some restrictions. Often used for group travel.
H = Higher level Economy Class with few restrictions.
I = Business Class Award and Upgrade
J = not in use
K = Discount economy fare with lots of restrictions. Typically used for intra-German oneways
L = Discount Fare Economy with a lot of restrictions
M = Almost Full Fare Economy with few restrictions, also used *A RTW
N = Non-revenue Economy Class
O = First Class Award and Upgrade
P = Non-revenue First Class, but not in use (?)
Q = Discount Economy with moderate restrictions.
R = Non-revenue Business Class
S = Ready-To-Fly economy class intra-Europe, negotiated fares like L'Tur
T = Heavy discount Fare Economy - often with a lot of restrictions
U = Heavy discount Fare Economy - often with a lot of restrictions
V = Discount Fare Economy often with a lot of restrictions, lowest 100% mileage earning fare
W = Discount Fare Economy often with many restrictions
X = Economy Class Award
Y = Full Fare unrestricted Economy class
Z = Heavily discounted Business Class