  Granular material on an inclined plane will flow like a fluid if the angle
$\theta$ the plane makes with the horizontal is large enough. We employ a
modification of a hydrodynamic model introduced previously to describe Couette
flow experiments to describe chute flow down a plane. In this geometry, our
model predicts a jammed-to-flowing transition as $\theta$ is increased even
though it does not include solid friction, which might seem necessary to
stabilize a state without flow. The transition is driven by coupling between
mean and fluctuating velocity. In agreement with experiments and simulations,
it predicts flow for layers with a thickness H larger than a critical value
$H_{\rm stop}(\theta)$ and absence of flow for $H<H_{\rm stop}(\theta)$.
