I just looked up
UA's contract of carriage. It's 49 pages, written in all caps. The only time security is mentioned is on page 9, one sentence.
SEARCH OF PASSENGER -
B) SEARCH OF PASSENGER OR PROPERTY--WHO REFUSES TO PERMIT SEARCH OF
HIS/HER PERSON OR PROPERTY FOR EXPLOSIVES OR A CONCEALED, DEADLY, OR
DANGEROUS WEAPON OR ARTICLE.
Not only is this one sentence largely hidden in the middle of an unreadable contract, you don't have to read it when purchasing a ticket. I don't know that having this hidden statement in a contract you're not required to read before purchasing a ticket could be considered informed consent to something as invasive as a strip search or patdown.
The statement also only says they will not carry people "who refuses to permit search . . . ." It does not specify that you have to permit any sort of search for explosives. Because it doesn't specify what type of search, I think an argument could be made that any consent you might be giving to be searched is to a "reasonable search."