Major flagellin required for motility. Not involved in PibD-dependent surface adhesion. Much more abundant in cells compared to FlgA2. Glycosylated by a pentasaccharide similar to the S-layer glycoprotein, probably comprising a hexose, 2 hexuronic acids, a methyl ester of a hexuronic acid and mannose. Glycosylation is required for biosynthesis of stable flagella. Cells are non-motile. Cells lacking both flgA1 and flgA2 show defects in motility, whitout affecting surface adhesion ability. Belongs to the archaeal flagellin family.