  We consider the variation of the field-induced component of the specific heat
$C({\bf H})$ with the direction of the applied field in $Fe-$pnictides within
quasi-classical Doppler-shift approximation, with special emphasis to recent
experiments on FeSe$_{0.4}$Te$_{0.6}$ [Zheng et al., arXiv:1004.2236]. We show
that for extended $s-$wave gap with no nodes, $C({\bf H})$ has $\cos 4 \phi$
component, where $\phi$ is the angle between ${\bf H}$ and the direction
between hole and electron Fermi surfaces. The maxima of $C({\bf H})$ are at
$\pi/4$, $3\pi/4$, etc. if the applied field is smaller than $H_0 \leq 1T$, and
at $\phi =0, \pi/2$, etc. if the applied field is larger than $H_0$. The
angle-dependence of $C({\bf H})$, the positions of the maxima, and the relative
magnitude of the oscillating component are consistent with the experiments
performed in the field of $9T >> H_0$. We show that the observed $\cos 4 \phi$
variation does not hold if the $s-$wave gap has accidental nodes along the two
electron Fermi surfaces.
