# Data-Driven Health Assessment in Flight Control System
## 3 Health Assessment Model and Comprehensive Health Index
### Health Assessment Model  
Flight control system is generally composed of main and auxiliary control system. The main control system uses the different control surfaces to complete the pitch, roll, and yaw motion; for the viewpoint of system operation, it can be divided into pitch, roll, and yaw channels. Furthermore, the auxiliary control system is used to carry out lift enhancement and other auxiliary functions. The failure mode analysis shows thatthe flight safety is mainly impacted by the main control system and the flaps in the auxiliary control system. In this paper, the system health assessment model is constructed by four channels, e.g., the three main channels and flap channel, which can be shown in Figure 1.  
In this figure, based on system analysis and flight monitoring parameters selection, thecharacteristic parameters can be extracted to reflect each channel's health state. Furthermore, the weight of each channel's characteristic parameters are given by rough sets reduction and the health assessment is completed at the different channels with fuzzy comprehensive evaluation. Finally, the comprehensive integration is carried out at the flight control system level to get the total quantitative assessment of system health state. Four channels' characteristic parameters are selected according to Failure Mode and Effect Analysis (FMEA) of flight control system, which is shown in Tables 1 and 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & **Failure Mode** & **Reason of Failure** & \begin{tabular}{c} **Influence on** \\ **System** \\ \end{tabular} & **Influence Degree** \\ \hline Steering wheel & stuck & Bolts are over tightened. & Aileron stuck & II \\ \hline Steering column & assembly stuck & \begin{tabular}{c} Bolts are over tightened, \\ rotating bearing is dry and \\ worn. \\ \end{tabular} & Elevator stuck & II \\ \hline Rocker & \begin{tabular}{c} Component \\ disconnected \\ \end{tabular} & Connector break & \begin{tabular}{c} Flight control \\ system failure \\ \end{tabular} & I \\ \hline Tie rod & Tie rod break & \
\begin{tabular}{c} Cracks and scratches on tie \\ rod pipes \\ \end{tabular} &
\begin{tabular}{c} Main control \\ system failure \\ \end{tabular} & I \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Failure Mode and Effect Analysis (FMEA) of the main control system (part). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & **Failure Mode** & **Reason of Failure** & \begin{tabular}{c} **Influence on** \\ **System** \\ \end{tabular} & **Influence Degree** \\ \hline Transmission & \begin{tabular}{c} Flaps are not \\ synchronized on \\ both sides \\ \end{tabular} & \begin{tabular}{c} Transmission \\ components \\ fracture \\ \end{tabular} & Flaps’ retraction & III \\ \cline{2-5}  & \begin{tabular}{c} Transmission \\ components stuck \\ \end{tabular} & \begin{tabular}{c} Spline or cross joint \\ stuck \\ \end{tabular} & Flaps cannot be & III \\ \hline Actuator & \begin{tabular}{c} Actuator \\ transmission \\ failure or stuck \\ \end{tabular} & Gears are worn & \begin{tabular}{c} Transmission \\ components are \\ stuck and flaps \\ cannot be retracted \\ \end{tabular} & III \\ \hline Flap position signal mechanism & \begin{tabular}{c} Flap position signal \\ mechanism does \\ not work \\ \end{tabular} & \begin{tabular}{c} Circuit is blocked \\ or the switch is in \\ poor contact \\ \end{tabular} & Flaps cannot be & III \\ \hline Fulcrum bearing of & \
\begin{tabular}{c} Transmission \\ components \\ deform and \\ become stuck \\ \end{tabular} &
\begin{tabular}{c} Transmission \\ component is stuck \\ and the flaps \\ cannot be retracted \\ \end{tabular} & III \\ \hline \hline \end{tabular}
\end{table} 
Table 2: FMEA of the flap system (part). Figure 1: Health assessment model. Therefore, the following three transmission coefficients are selected as parameters that characterize the health status of the main control system:  
1. Pitch channel: steering column to elevator transmission coefficient. 2.