# A Study of Emergency Aircraft Control During Landing
## 9 Conclusions  
The impact of measurement noise filtering on the control system's performance was beyond the scope of this study. Although the inherent signal transport delay associated with the research platform's limitations may produce similar effects, further system development should include a more comprehensive analysis of system stability, particularly with respect to this issue. The thrust control system concludes its operation by applying the brakes once the wheels contact the runway. The aircraft's movement during the landing rollout--where it decelerates to a complete stop--is not addressed in this paper. Maintaining the aircraft within the runway centreline during braking is a separate control problem, which is particularly relevant under crosswind conditions. Controlling the aircraft during the landing phase could be achieved with an additional module that manages engine thrust, including engagement of the thrust reversers. The goal of such a module would be to minimise lateral deviation from the centreline, based on measurements from the onboard inertial navigation system (INS) or the ILS localizer signal,as used in this work. Developing a control law for this purpose would require knowledge of the aircraft's dynamics on the runway, which change as speed decreases. This would necessitate the use of gain scheduling in the control loop. An additional challenge lies in the non-linear relationship between the thrust lever position and the resulting reverse thrust. Establishing an accurate aircraft dynamic model based on simulator trials may be difficult; therefore, constructing such a model would require detailed knowledge of the aircraft's structural parameters--such as moments of inertia for the airframe components--and an approximation of the reverse thrust corresponding to specific thrust lever positions. The emergency thrust control system proposed in this paper was fine-tuned for two specific configurations of the studied aircraft. When discussing the potential generalisation of the developed control algorithm to other aircraft types and scenarios, several factors must be considered. Firstly, the dynamic characteristics of a particular aircraft in a given configuration can vary significantly--not only between different aircraft types but also within the configurations of a single model due to changes in the flaps setting, landing gear extension, gross weight, or centre of gravity position. This aspect has been previously studied by NASA Dryden, who tested their PCA system on a variety of aircraft models (as mentioned in Section 2). The use of linear-quadratic optimisation to compute LQRI controller settings can help normalise control dynamics across multiple configurations of a single aircraft, but not between different aircraft types. Ultimately, the values of \(\mathrm{K_{lqri}}\) and \(\mathrm{F_{lqri}}\) matrices are specific to a single aircraft configuration. It is the integral action that provides a degree of robustness to certain changes around the tuned configuration. A key limitation when it comes to generalising the developed system is the need to subtract steady-state constants from the measured feedback signals of the flight path angle controller to obtain the increments of airspeed (\(\mathrm{u_{EAS}}\)), angle of attack (\(\alpha\)), and pitch angle (\(\theta\)), as well as to compute the steady-state thrust lever positions (\(\delta\mathrm{T_{0}}\)). As discussed in Section 5.3, the values of these constants are characteristic of a given configuration but can also change during flight--primarily due to factors such as fuel consumption. For the system to operate correctly across a broader, or even complete, range of aircraft configurations, these constants must be determined, preferably directly and without the need for additional flight trials, which would otherwise make system generalisation impractical. Several approaches can be considered to address this issue. One possibility is developing a method for filtering out unknown, transient constant values from the feedback signals.