Actuators used to move the wing slats on Embraer 170s have been redesigned as a consequence of a fault discovered by airline operators in Australia and elsewhere.

The Australian Transport Safety Bureau says that since the fault has been discovered, the slat actuator manufacturer has initiated a redesign of the actuator "to reduce torque trip and limiter engagement".

Meanwhile, "the aircraft manufacturer has issued a new fault isolation task to address the fault and stop recurrence", it says.

The safety bureau and Australian carrier Virgin Blue discovered the fault in 2008.

The bureau says that on 10 August a Virgin Blue E-170, local registration VH-ZHA, was operating from Sydney to Melbourne with six crew and 54 passengers on board.

"During the approach into Melbourne, the flightcrew selected the flaps to 'flaps 1' [but] when the selection was made, a number of caution messages including 'slat fail', 'spoiler fault', 'aircraft operating angle of attack limit fail' and 'shaker anticipated', appeared. The flaps were cycled up and down, again with the caution messages reappearing."

It says the pilots eventually landed the aircraft and an examination on the ground by the airline's engineers "identified a slat jammed/under speed fault".

The bureau adds: "The appropriate fault isolation manual task was completed and it was found that the left side number 3 slat actuator torque trip limiter had actuated."

The documentation "revealed that this usually occurs when the slats are operated in extremely cold conditions".

It adds that the airline operator then contacted another E-170 operator overseas that uses E-170s in cold climates, and that operator "informed the operator of VH-ZHA that they experienced slat/flap failures weekly and at times daily".

Source: Flight International