In order to book an upgradable fare on United you have to buy a ticket in fare class W or higher. Here are the fare classes above W.
V
Q
H
U
E
M
B
Y
Only airlines could convolute something so simple as the ordering of the alphabet.
Related
Given the early mission of the internet to democratize information,
Pudits like to point to apps (and importantly the availability
I read recent coverage of comments from Carnegie Mellon University