Tex. Gov't Code § 1503.154

As additional security for the encumbrance, a municipality that encumbers an airport under Section 1503.153 may provide in the encumbrance for a grant, to the purchaser under sale or foreclosure, of a franchise to operate the airport and the improvements situated on the airport for a term not to exceed 30 years from the date of the purchase, subject to all laws regulating same then in force.