In answer to my own question, I searched the web and found this:Fare Classes and Codes
Class Description
A Full-fare First Class
C Full-fare First Class on International flights with no BusinessFirst
D Domestic Upgrade portion of BusinessFirst itinerary (or discounted BizFirst)
E Reward First Class and Upgrade BusinessFirst
F Upgradeable First Class
Y Full-fare, unrestricted refundable coach
H Slightly Discounted non-refundable coach
K Non-Refundable Coach
B Non-Refundable Coach
V Non-Refundable Coach
Q Non-Refundable Coach
T Non-Refundable Coach (this class is used to match low fare carrier fare sales and is the cheapest available)
U Easypass BusinessFirst

Domestic
All fares can be upgraded. Elite and mileage upgrades come from F. Gold and Platinum Y-fare upgrades come from A. Onepass mileage upgrades come from E.

International
International flight classes J, D, and Z replace A, D, and F, respectively. BusinessFirst seats for upgrades is a class R which does not show in ITN but is equivalent to Z at most times. H and K fares are upgradable to R class. Y fares are upgradable to Z class.
Sometimes, Z can be a highly discounted BusinessFirst fare.

Misc
V, Q and T are usally excluded from promotions and bonuses

Fare Codes
Fare codes beginning wth "QL" are refundable. Having "NR" or "IP" at the end of a fare code is an indication that the fare is non-refundable.


dbaker


here:

http://www.ityt.com/library/?_recurse=1&file=21

(thanks dbaker)