One of the members on this forum was an airport police officer, until recently.
The officers' radios at the airport are programmed for the Charlotte-Mecklenberg trunked system - including the talkgroups you refer to, Soundman - but BlindDog is correct ... they do not use the talkgroups. Instead, they use a conventional repeater on 800 that has some decent range beyong the airport property.
Besides the frequency mentioned by BlindDog, there are two other channels that are used for non-public safety operations at the airport. All three are listed on Radio Reference at:
http://radioreference.com/modules.php?name=RR&aid=2034
Although not listed, the non-public safety channels also use a PL tone of 131.8 Hz.