My roommate just booked a ticket using UA miles on UA, US, AC, and LH. His UA account has his name as Tim, so that's what the ticket says. His passport says Timothy. He was able to enter Timothy on the TSA Secure Flight section where it says the name must match. Should there be any issues?

No. The principle here is one of "consistency", not neccesarily "identical-ness".

Dave

Tim is not a nickname for someone called Timothy. That is called a dimunitive. Rob for Robert (thought the Brits use Bob), Tim for Timothy, Joe for Joseph. Not a big deal.

Now if I used my nickname from college, Gramps, then I might have a problem

Should there be? No.


Will there be? It depends on the whim of whichever TDC you encounter. My spouse got hassled because the name on her ticket did not exactly match the name on her passport. I should note that the difference was inconsequential and it would be obvious to anyone with more than 6 functioning brain cells that there should be no problem. Without giving away her name the difference was along the lines of:

Ticket said:............Passport said:

Jan ..................... Janet
Nita ..................... Anita
Sue ......................Susan

One would think that a trained TDC could comprehend that this should not be a big deal. However; TSA seems to prove every day that there is not such thing as "too stupid to work here".

As was pointed out before, this is more an abbreviation than a "nickname". I think the best answer is that it shouldn't matter, but there are ample opportuntities where it might. There are more chances it might matter on international flights than domestic simply because more people are looking at ID. It's indeed good to put the full name in the SFPD as well as AFIS (if international), as you've done. But I'd also strongly suggest updating the name in the UA account: this is a quite routine request of airlines and one they encourage. I doubt they'd change the name on this ticket, but at least it won't be a problem in the future.

I had one TSO at the podium in ATL point out the my BP was for Chris and my Passport said Christopher. I joked that only my mother had ever called me Christopher but she didn't crack a smile and told me that it could keep me from getting through security in the future and that the names must match exactly and that I should address it.

Never happened before then and never after.

...from future problems: barking TDCs, polite but still lecturing German offciers, etc.)

(In other parts of the world people less frequently use abr or nickname on official papers.)

With so many miles I assume your friend has some status? So he can call UA ff line, and change his first name to its long version on his ff account in 3 min - for future travels.