Contingent capital, a device that grew from financial engineering, is a major new idea that might fix the problem of banking instability, thereby stabilizing the economy – just as devices invented by mechanical engineers help stabilize the paths of automobiles and airplanes. If a contingent-capital proposal is adopted, this could be the last major worldwide banking crisis – at least until some new source of instability emerges and sends financial technicians back to work to invent our way of it.