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Motivation

There is an increasing trend in the designs of new aircraft and spacecraft to move to fly-by-wire controls and away from the more traditional hydraulic control and actuation methods. There are several types of actuation mechanisms being utilized in such fly-by-wire designs, such as electro-mechanical actuators. Actuators are usually some of the more safety-critical components of an aerospace system, and hence, an undetected or unmanaged actuator failure can lead to serious consequences. For instance, the tragedy of Alaska Airlines MD-83 Flight 261 occurred due to horizontal stabilizer electromechanical actuator failing because of insufficient lubrication and excessive wear of its jack screw.

Even though actuators have been studied extensively from a functional point of view – in order to help develop new and improved designs – studies from a health management point of view have been rather limited. The reason for that is largely attributed to unavailability of operational fault data from fielded applications and lack of experimental studies with seeded fault tests due to high risks and costs involved. EMAs in aerospace systems operate in complex environmental conditions, so their inherent characteristics need to be studied thoroughly in order to be distinguishable in flight environment and enable effective diagnostics and prognostics with reduced uncertainty. This calls for a systematic, methodical effort towards understanding the EMAs and their behavior under various fault conditions through affordable, but realistic experiments.

Jackscrew 261 Still Sm
A screen shot from the MD-80 horizontal stabilizer computer simulation
(Source: National Transportation Safety Board)

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