  The first proof of well-posedness of an initial boundary value problem for
the Einstein equations was given in 1999 by Friedrich and Nagy. They used a
frame formalism with a particular gauge for formulating the equations. This
`Friedrich-Nagy' (FN) gauge has never been implemented for use in numerical
simulations before because it was deemed too complicated. In this paper we
present an implementation of the FN gauge for systems with two commuting
space-like Killing vectors. We investigate the numerical performance of this
formulation for plane wave space-times, reproducing the well-known Khan-Penrose
solution for colliding impulsive plane waves and exhibiting a gravitational
wave `ping-pong'.
