Catalyzes the reversible formation of fructose 6-phosphate from dihydroxyacetone and D-glyceraldehyde 3-phosphate via an aldolization reaction. Can utilize hydroxyacetone as an alternative donor substrate. Is also able to catalyze the direct self-aldol addition of glycolaldehyde. Is less catalytically efficient than the isozyme FsaA. Does not display transaldolase activity. beta-D-fructose 6-phosphate = D-glyceraldehyde 3-phosphate + dihydroxyacetone Catalytic efficiency is 28-fold higher using glyceraldehyde 3-phosphate as acceptor substrate and hydroxyacetone as donor substrate than with dihydroxyacetone as the donor. Optimum pH is 8.5 for the retroaldol activity on F6P. Is not thermally stable at temperatures higher than 60 degrees Celsius. Is less thermostable than the isozyme FsaA. Homodecamer. Belongs to the transaldolase family. Type 3A subfamily.