Let $e_1$ be the eccentricity of the hyperbola $\dfrac{x^{2}}{16}-\dfrac{y^{2}}{9}=1$ and $e_2$ be the eccentricity of the ellipse $\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$ ($a>b$), which passes through the foci of the hyperbola. If $e_1e_2=1$, then the length of the chord of the ellipse parallel to the $x$-axis and passing through $(0,2)$ is: