"Hi, I have a question. I have an outstanding warrant and am going to be flying from CA to NV in the next month. I was just wondering if airlines (in particular, Southwest) does background checks or something with your id when you check in?"
*** No. The airlines do not have any 'police' authority. Any screening is done under the auspices of the TSA (Transportation Security Administration). The following comes from their website:
" Myth: CAPPS II will run a criminal background check on every passenger.
Fact: No, CAPPS II will NOT run a criminal background check on every passenger. Instead, CAPPS II will perform an identity authentication and a risk assessment. Specifically, CAPPS II will do two things:
It will assess the identity of every passenger by matching limited information about the traveler, including name, date of birth, address, and phone number, with commercially available information. This check is done between databases outside of a government firewall. CAPPS II will not bring any information contained in the commercial databases into the government's system.
CAPPS II also performs a risk assessment, including a check against lists of terrorists and known or suspected threats, to detect individuals who may pose a terrorist-related threat or who have outstanding Federal or state warrants for crimes of violence.
Myth: If a passenger has several speeding tickets or misdemeanors on his/her record, does this mean that he or she cannot fly?
Fact: No, a speeding ticket or misdemeanor in and of itself will not bar a passenger from flying. CAPPS II will assess a passenger's identity and perform a risk assessment. The aggregated information will determine screening level. In the rare instances where a particular traveler has been identified as having known or suspected links to terrorism, or an outstanding warrant for violent criminal behavior, appropriate law enforcement officers will be notified."
Source:
http://www.tsa.gov/public/display?content=09000519800626f4
"Can I be arrested on the spot?"
*** In the extremely unlikely chance that a passenger is found to be a risk, that passenger MAY be detained and local authorities (police, etc.) be contacted.
So, unless you plan on standing in the middle of the airport and making terroristic threats of retaliation for your outstanding warrant(s), the chance of your being detained due to that warrant are somewhere between zero and nil.