Answer
$$
63.3 \mathrm{m} / \mathrm{s}
$$
Work Step by Step
The plane's speed relative to the air is
$$
v=\sqrt{\frac{2 \rho g h}{\rho_{\text {air }}}}=\sqrt{\frac{2\left(810 \mathrm{kg} / \mathrm{m}^{3}\right)\left(9.8 \mathrm{m} / \mathrm{s}^{2}\right)(0.260 \mathrm{m})}{1.03 \mathrm{kg} / \mathrm{m}^{3}}}=63.3 \mathrm{m} / \mathrm{s}
$$
