Within the contents of this paper, trough application of Business Intelligence, the resolution of one of the fundamental business problems of Zagreb International Airport, passenger aircraft delays, is addressed. In the second chapter of this paper, the concept of Business Intelligence, application areas, implementation methods, concepts, reasoning and working principle of such systems are described. In chapter three, a description of the principle, and the use of data mining methods, which are the functioning basis of most Business Intelligence systems is offered. The methodology of preprocessing, search, validation, and data cleaning in the process of data mining is presented, which is necessary to obtain relevant information and knowledge in large data sets, as well as proper implementation of the Business Intelligence model. Furthermore, methodology of learning, and the creation of inductive rules is described, which are chosen to address the problem of model estimation of passenger aircraft delay through Zagreb International Airport. The practical part of this paper presents the development of a model estimation of passenger aircraft delay, based on real data about the delay of the aircraft, in the period between 2009. and 2011. Also, a segmentation of the model in several key sub-processes is described, such as preprocessing, construction and evaluation of models for estimating the delay of passenger aircraft. Finally, some key (but not only) possible model application areas for delay estimation are suggested, such as better passenger building employees working hours planning, and acquiring advantages in contract negotiations with airlines.