This paper presents a novel methodology for the design of motion controllers for UAV's of quad-rotor type. The developed controllers are of time switching type, where discrete modes are determined by the momentary availability of global positioning information. Relevant application scenarios are found, where the availability of GPS or generally GNSS is scarce, e.g. in case of indoor flight. For indoor flight dedicated indoor positioning technology may be applied, such as the ultra-sound/radio solution from . Even with such technology available, due to reflection, interference and absorption, the required positioning service cannot be provided continuously without intermittency. A control model is presented, for which a general observer based controller framework is suggested. Feedback and observer gains are then allowed to switch according to the availability of positioning information. The mechanical states of the UAV are inherently un-observable in the absence of positioning information. Therefore the controller, in that case, will be unstable. However, by designing a set of feedback/observer gains to obtain stochastic stability under a given stochastic model for the switching process, an overall well functioning controller is obtained.