During the test run of large turbo fan engines in the newly instated test cell of the Korean Air Lines, an engine stall occurred repeatedly at high thrust settings. Flow field measurements within the test cell, 1/40 scale model testing and performance analysis of the test cell were performed in order to determine the cause of the stag and to find a quick remedy. Based on the results of these studies a corrective measures, which led to a satisfactory test cell performance, were taken. This paper presents the method of approach to the problem, results of the cell flow field measurements and the model testing, an improved analytical method to predict the test cell performance, and the modified configuration of the test cell. The present analytical procedure and some of the test data can be used for design and analysis of other engine test cells.