In aerodynamics, the Crow Instability or V.C.I vortex crow instability is an inviscid line-vortex instability, named after its discoverer S. C. Crow. The Crow instability is most commonly observed in the skies behind large aircraft such as the Boeing 747. It occurs when the wingtip vortices interact with contrails from the engines, producing visible distortions in the shape of the contrail.