I DEALING with the stress analysis of the side panel of a welded steel-tube aircraft fuselage, or of any similar framework, two independent questions arise. First, the stresses due to the axial forces, and to the bending moments caused by couples or by external loads applied between joints, must be checked against the allowable values. Second, it must be ascertained tha t the magnitude of the applied load system is smaller than the first critical (buckling) load of the structure. The actual calculations involved in the first question are relatively simple. Any standard method based upon the assumption of pin joints may be used in computing the axial forces. To determine the bending moments in the bars James 's adaptat ion of the Hardy Cross method 1 is usually simplest. Methods for treat ing the stability problem have been suggested by von Mises, Teichmann, Borkmann, Prager, the author and Lundquist. In the present paper a criterion is developed whereby the work necessary for the stress analysis of a plane framework is materially reduced. This criterion is as follows: If James 's version of the Hardy Cross method is used in the calculation of the distribution of the bending moments in the bars, and a finite, unique set of values is obtained, then this result is a necessary and sufficient condition for stability. Consequently, if the bending moments in the bars have been calculated by James's version of the Cross method, which is incidentally the simplest procedure to obtain these indispensable values, by the criterion proved in this paper, any further check of the stability is superfluous.