In the paper we consider a model for the representation and processing of procedural knowledge of an intelligent unmanned aerial vehicle (UAV) that is based on the logic of condition-dependent predicates. Condition-dependent predicate calculus provides logically valid inferences in an arbitrary subject area by isolating monotone regions. The proposed knowledge model contains a set of frame-based microprograms of behavior (FMP) and overcomes certain disadvantages of known logic models. Procedures for planning purposeful behaviour of an unmanned aerial vehicle in underdetermined environment are proposed.The automatic planning of the purposeful UAV behavior in an underdetermined environment comes down to: substitution of objects for subject variables that implement slots functions in condition-dependent predicates and form the structure of FMP body; planning of purposeful activity through verification of conditions that determine possibility of efficiently performing operations included in the FMP structure and by selection of typical elements of procedural knowledge. In the experimental part of the paper we simulate UAV purposeful behaviour in a perturbed environment. Copyright © 2018 for the individual papers by the papers’ authors.