The crisis with the planes peaked when some had to make emergency landings after problems developed with the landing gear.
The first investigation showed that 25 of the 27 planes had rust damage which was undetectable if only inspected from the outside.
Now according to a report in newspaper Svenska Dagbladet, the ongoing investigation has shown faults with the hydraulic systems.
So far this problem has been detected in 16 of the 18 planes inspected. SAS would not have had the possibility to inspect for the problems since a full inspection only occurs every ten years, and the Dash-8 plans were bought in 2000.