Absolute stability region
Stable region in red.

Coefficients

\begin{align} \begin{array}{c|ccc} & \frac{1}{6} & - \frac{1}{3} & \frac{1}{6}\\ \frac{1}{2} & \frac{1}{6} & \frac{5}{12} & - \frac{1}{12}\\ 1 & \frac{1}{6} & \frac{2}{3} & \frac{1}{6}\\ \hline & \frac{1}{6} & \frac{2}{3} & \frac{1}{6} \end{array}\end{align}

Properties