for UA

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 RTW fares
E = 1K Special Economy Class Award (inventory available only to 1K pax)
F = Full Fare Unrestricted First Class
G = Travel Industry Economy Class fares
H = Higher level Economy Class usually with few restrictions. RTW coach is in H
I = Business Class Upgrade class from Economy (Better known as 'NC' class)
K = Seasonal Economy Promotional Fares/Reduced Fare Gov’t contract etc
L = Discount Fare Economy with a lot of restrictions
M = Almost Full Fare Economy with few restrictions
N = Economy Class AWARD TICKET (Better known as 'XY' class)
O = Business Class AWARD TICKET (Better known as 'XC' class)
P = Premium USA Transcon First Class on 3 classers
Q = Discount Fare Economy often with moderate restrictions
R = First Class AWARD TICKET (Better known as 'XF' class)
S = Real Lowball Economy with lot of restrictions. Not always mile earning
T = Discount Fare Economy often with a lot of restrictions
V = Discount Fare Economy often with a lot of restrictions
W = Discount Fare Economy often with many restrictions
X = First Class UPGRADE AWARD from paid Business (Better known as 'NF')
Y = Full Fare unrestricted Economy class