Canadian regulatory authorities have issued a formal airworthiness directive calling for all Bombardier Dash 8 Q400 operators to conduct immediate landing gear inspections following two incidents involving Scandinavian Airlines (SAS) aircraft.

Bombardier says in a statement that Transport Canada has issued an airworthiness directive that requires all operators of Q400s to conduct a "general visual inspection" of the left and right main landing gear system as well as main landing gear retract actuator jam nut on each turboprop aircraft.

It also calls for an immediate "detailed visual inspection" of the main landing gear retract actuator on actuators that have accumulated 8,000 or more landings or have been in service for more than four years, whichever comes first.

"Bombardier estimates that this affects approximately 85 Q400 aircraft," says the Canadian manufacturer, adding that "newer actuators will also be inspected with varying timelines depending on the age of the actuator".

Bombardier Regional Aircraft president Steven Ridolfi says: "We understand that this proactive measure will unfortunately inconvenience many of our customers and their passengers. However safety remains our primary concern. We are working diligently with our customers to ensure the affected aircraft return to revenue service as quickly as possible."

Yesterday Bombardier and landing gear manufacturer Goodrich called for operators of Q400s with more than 10,000 cycles to be grounded pending landing gear inspections, affecting around 60 Q400 turboprops out of a global fleet of more than 160.

The call came after an SAS Q400 suffered a right main landing gear collapse at Aalborg in Denmark on 9 September and another at Vilnius in Lithuania on 12 September.

"Bombardier has sent two separate air safety teams to the sites of the two recent incidents to assist in the investigations involving the Q400 aircraft operated by SAS," says the airframe manufacturer.

"Bombardier continues to provide its support to the investigations being conducted by the Danish and Canadian regulatory authorities. Until such time as investigations are concluded by the relevant aviation authorities, Bombardier cannot speculate as to the cause of these incidents."