  Context. The dynamics of the flaring loops in active region (AR) 11429 are
studied. The observed dynamics consist of several evolution stages of the
flaring loop system during both the ascending and descending phases of the
registered M-class flare. The dynamical properties can also be classified by
different types of magnetic reconnection, related plasma ejection and aperiodic
flows, quasi-periodic oscillatory motions, and rapid temperature and density
changes, among others. The focus of the present paper is on a specific time
interval during the ascending (pre-flare) phase. Aims. The goal is to
understand the quasi-periodic behavior in both space and time of the magnetic
loop structures during the considered time interval. Methods.We have studied
the characteristic location, motion, and periodicity properties of the flaring
loops by examining space-time diagrams and intensity variation analysis along
the coronal magnetic loops using AIA intensity and HMI magnetogram images (from
the Solar Dynamics Observatory(SDO)). Results. We detected bright plasma blobs
along the coronal loop during the ascending phase of the solar flare, the
intensity variations of which clearly show quasi-periodic behavior. We also
determined the periods of these oscillations. Conclusions. Two different
interpretations are presented for the observed dynamics. Firstly, the
oscillations are interpreted as the manifestation of non-fundamental harmonics
of longitudinal standing acoustic oscillations driven by the thermodynamically
nonequilibrium background (with time variable density and temperature). The
second possible interpretation we provide is that the observed bright blobs
could be a signature of a strongly twisted coronal loop that is kink unstable.
