  We present preliminary results on on-sky test of sky subtraction methods for
fiber-fed spectrograph. Using dedicated observation with FLAMES/VLT in I-band,
we have tested the accuracy of the sky subtraction for 4 sky subtraction
methods: mean sky, closest sky, dual stare and cross-beam switching. The cross
beam-switching and dual stare method reach accuracy and precision of the sky
subtraction under 1%. In contrast to the commonly held view in the literature,
this result points out that fiber-fed spectrographs are adapted for the
observations of faint targets.
