Rockwell Collins' California-based Kaiser Electroprecision, working as part of Parker Aerospace's overall integrated flight control, fuel and hydraulic systems responsibilities on the 170/190, has developed and patented a safety device on the horizontal stabiliser trim actuator (HSTA) assembly. The HSTA is a linear electromechanical ball screw actuator powered by dual brushless 28V DC motors on the 170 and by 270V DC motors on the 190. Kaiser planned to use a common HSTA for the 170 and the 190, but the change in the larger aircraft's empennage resulted in a 50% size increase.

"It normally takes 18 to 24 months to make a change like that, but this was done in less than six," says Tony Najjar, Kaiser Electroprecision general manager. The design incorporates an innovative, spring-energised, secondary split nut which will trigger "in case of a primary load path failure, and will lock up the actuator", says Najjar. The 170/190 is the first application for the concept, which was developed in the wake of the Alaska Airlines Boeing MD-80 accident caused by a horizontal stabiliser jack screw failure.

"If there is linear motion in the primary load path, a rack-and-pinion slide mechanism goes down and triggers the split nut that locks up the actuator," he adds, pointing out that the aircraft will remain controllable even with the stabiliser at high angles of deflection. The safety device is highlighted in the diagram (left) in red.

Source: Flight International