Gaseous S(VI) (SO3 + H2SO4) has been measured by chemical ionization mass spectrometry (CIMS) in the simulated internal flow of an aircraft gas turbine in a test rig at ground level during the PartEmis 2002 campaign. Building on S(VI) and calculated total sulfur ST the abundance ratio ϵ = S(VI)/ST was determined. The measurements to be reported here were made at two sampling points, for two engine test conditions representative of old and modern aircraft cruise and for a fuel sulfur content FSC = 1270 ppm. For both cruise conditions the measured ϵ increased with increasing exhaust age from the high pressure to the low pressure stage. For each pressure stage ϵ was higher in the modern cruise condition. The maximum ϵ (2.3 ¿ 1.2%) was obtained for modern cruise and the low pressure stage. Our present data suggest that modern engines have a somewhat higher conversion efficiencies than old engines.