  We studied waves seen during the class C1.9 flare that occurred in Active
Region NOAA 11272 on SOL2011-08-17. We found standing waves with periods in the
9- and 19-minute band in six extreme ultraviolet (EUV) wavelengths of the
SDO/AIA instrument. We succeeded in identifying the magnetic arc where the
flare started and two neighbour loops that were disturbed in sequence. The
analysed standing waves spatially coincide with these observed EUV loops. To
study the wave characteristics along the loops, we extrapolated field lines
from the line-of-sight magnetograms using the force-free approximation in the
linear regime. We used atmosphere models to determine the mass density and
temperature at each height of the loop. Then, we calculated the sound and
Alfv{\'e}n speeds using densities $10^8 \lesssim n_i \lesssim 10^{17}$
cm$^{-3}$ and temperatures $10^3 \lesssim T \lesssim 10^7$ K. The brightness
asymmetry in the observed standing waves resembles the Alfv{\'e}n speed
distribution along the loops, but the atmospheric model we used needs higher
densities to explain the observed periods.
