As soon as 1932, Jan Tinbergen proposed an explanation of the Great Depression based on a specific treatment of unstable processes and multiple equilibria. After his involvement in the early meetings of the Econometric Society, he worked on different dynamic models accounting for this instability. In 1934, he built a macrodynamic model generating new types of economic movements that did not return to a stationary state. This led him in 1936 to consider the possibility of having two equilibria, with damped or self-sustained cycles around the high equilibrium and a collapse around the low equilibrium. Tinbergen saw these models, with reference to Irving Fisher's 1933 paper, as a way to interpret the potential of a crisis to trigger the collapse of the economy. In the end, it turns out that Tinbergen managed to extend the perspective for the study of the business cycle mechanism to non cyclical behaviours which, strikingly, remains almost totally ignored in most histories of macroeconomics and econometrics.