# A Study of Emergency Aircraft Control During Landing
## 6 Control System
### Architecture of Emergency Thrust Control System  
The proposed emergency thrust control system consists of modules performing the following functions:  
* Computation of thrust lever position in steady state. * Heading setpoint conversion. * Flight path angle control. * Heading control. * Control signal mixing. * Glide path tracking. A simplified diagram of signal connections between the modules is shown in Figure 5a. The thrust lever position computing system employs the function described in Section 5.3.3. Based on the measurements of \(\mathrm{P_{amb}}\) and \(\mathrm{T_{amb}}\) the thrust lever position \(\delta T_{0}\), corresponding to the flight's aerodynamic steady state, is determined as a base signal for controlling the aircraft's engines. The heading setpoint conversion module is responsible for computing the heading angle error passing on the input of the heading control system. The system determines the smallest angle between the heading setpoint \(\mathrm{HDG_{set}}\) and the current magnetic heading \(\mathrm{\Psi_{mag}}\), specifying, at the same time, the direction of turn in the range of [\(-180^{\circ}\); \(180^{\circ}\)]. The presented solution eliminates a problematic, from a control perspective, transition of heading from \(359^{\circ}\) to \(0^{\circ}\) when turning to the right and from \(0^{\circ}\) to \(359^{\circ}\) when turning to the left. The prepared module imitates the operation of navigation systems found in airliners. In comparison with the Simulink model prepared for the initial system tuning, two significant changes associated with the system adaptation to the aircraft's in-flight-simulator control were introduced into the structure of the flight path angle control module. The first change concerned the measurement signal processing. The adopted control method required each of the feedback signals to represent a value increment from a steady-state flight. Therefore, specific constant values had to be subtracted from the measured equivalent airspeed \(\mathrm{U_{EAS}}\), angle of attack \(\mathrm{\alpha_{abs}}\), and pitch angle \(\mathrm{\theta_{abs}}\). The second change involved the introduction of a dynamic thrust lever deflection limiter block. As the value of \(\mathrm{\delta T_{0}}\) signal varies with flight altitude, the available lower and upper lever deflection ranges are being defined. The heading control system performs the task of minimising the heading error \(\mathrm{\Delta HDG_{set}}\) computed by the heading conversion module. In the target structure of the designed system, in similar way to the flight path angle control, a dynamic limiter block was applied. The computation of instantaneous control output limits required defining a value of the narrower of available thrust lever deflection ranges. Another important role is filled by the module presented in Figure 3. Its task is to combine the control outputs of flight path (\(\mathrm{\delta T_{Ion}}\)) and heading (\(\mathrm{\delta T_{lat}}\)) control systems and to define direct control commands \(\mathrm{\delta T_{L}}\) and \(\mathrm{\delta T_{R}}\) for the thrust levers' absolute position. Figure 5b shows the glide path tracking system. It is designed to define the setpoints of flight path angle and heading to guide and track the glide path to a selected runway. The featured system performs its intended function according to the signals from the on-board ILS receiver and the altitude indications of the radio altimeter \(\mathrm{H_{agl}}\). The ILS signal inputs include heading towards the localizer \(\mathrm{\psi_{loc}}\), heading error \(\mathrm{\Delta\psi_{loc}}\), and distance from the localizer \(\mathrm{d_{DME}}\). The specific nature of emergency thrust control makes the ILS glideslope tracking alone insufficient for securing a safe landing.