Context. The role of magnetic helicity in active filament formation and destabilization is still under debate. Aims. Although active filaments usually show a sigmoid shape anda twisted configuration before and during their eruption, it is unclearwhich mechanism leads to these topologies. In order to provide anobservational contribution to clarify these issues, we describe afilament evolution whose characteristics seem to be directly linked tothe magnetic helicity transport in corona. Methods. We applied different methods to determine the helicitysign and the chirality of the filament magnetic field. We also computedthe magnetic helicity transport rate at the filament footpoints. Results. All the observational signatures provided informationon the positive helicity and sinistral chirality of the flux ropecontaining the filament material: its forward S shape, the orientationof its barbs, the bright and dark threads at 195?. Moreover, themagnetic helicity transport rate at the filament footpoints showed aclear accumulation of positive helicity. Conclusions. The study of this event showed a correspondencebetween several signatures of the sinistral chirality of the filamentand several evidences of the positive magnetic helicity of the filamentmagnetic field. We also found that the magnetic helicity transportedalong the filament footpoints showed an increase just before the changeof the filament shape observed in Himages. We argued that the photospheric regions where the filament wasrooted might be the preferential ways where the magnetic helicity wasinjected along the filament itself and where the conditions to triggerthe eruption were yielded. Key words: Sun: activity - Sun: filaments - Sun: magnetic fields
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