Power transmission line inspection is an essential task carried out by power companies for the maintenance of a power network. The lines are exposed to the elements which increases the rate of deterioration of small faults and when not repaired in a time efficient manner they can become a serious problem. Current methods for inspection are labour intensive, expensive and are tedious and error prone for humans to perform. A possible solution is a UAV to perform the dull, dirty and dangerous task of power line inspections. As of August 2013, 16 companies were listed with CASA as licensed UAV operators for the purpose of power line inspection. With the maturing of the UAV and related sensors the technology is now accessible to researchers to adapt UAV technology to power transmission line inspections. The next step in the maturing of the technology will be to prove reliability and gain human acceptance. This dissertation will research on UAV technology and present a method for controlling a UAV autonomously using visual navigation and analysing pictures taken in real time for the inspection of power transmission lines. The dissertation will research the combination of automation and picture analysis in a field environment.