# A Study of Emergency Aircraft Control During Landing
## 7 SIL Simulations
### Landing Attempts  
Performing a landing with frozen control surfaces requires maintaining an airspeed well above the predicted structural value. In the case of Boeing 757-200, the recommended approach speed is 132 kts in relation to the approximately 235 kts recorded during the SIL simulation of the system. In this context, a landing attempt with ILS-generated glide path, given the extended flight path settling time, will undoubtedly result in landing gear damage and the aircraft crashing. The developed glide path tracking module made it possible to adjust the course of an approach to the known dynamics of thrust control. For the purpose of conducted simulations, a glideslope of 2\({}^{\circ}\) was prepared, intersecting with the airport apron just before the runway threshold. The automatic approach attempts were carried out in the following sequence: stabilise the flight at an altitude of approx. 2500 ft (parallel to the runway centreline); execute a 180\({}^{\circ}\) turn in the direction of ILS localizer; and follow the glide path until the beginning of a flare manoeuvre, i.e., an increase in the angle of attack just before touchdown. Due to the control dynamics, the flare was initiated at an altitude of 150 ft. Figure 7a shows the approach trajectory and glide path (red dashed line) recorded during one of the landing attempts. With an approach flight path angle of \(\gamma=-2^{\circ}\), the landing aircraft is just below the standard ILS glideslope. Figure 8a shows the control parameters recorded during this attempt. Extending the landing gear as the aircraft comes out of a turn helps one to achieve a negative flight path angle. Starting from an altitude of 150 ft, the tracking module gradually increases the set flight path angle to \(-0.5^{\circ}\) at 50 ft, which, in combination with a presence of the ground effect, results in landing gear coming into contact with the runway surface at a flight path angle of approximately \(-0.35^{\circ}\). Figure 9a also shows the resulting tracking of a defined glide path. In order to determine the overall control robustness to possible disturbances, the ability to safely perform the manoeuvre and the difficulties associated with its realisation, some of the landing attempts were carried out in windy conditions. The X-Plane simulator allows the scheduling of weather conditions with parameters such as general wind speed and  
Figure 7: Trajectory of landing approaches: (**a**) in windless conditions; (**b**) in crosswinds of 14 kts. direction, gust speed changes, and the presence of windshear. The recorded landing attempt was performed under conditions of 110\({}^{\circ}\) wind direction at a speed of 14 kts with gusts up to 17 kts and windshear in a range of 18\({}^{\circ}\). For the aircraft landing on a 182\({}^{\circ}\) heading, this was effectively a wind blowing from the left (Figure 7b). Figure 8b shows the recorded control parameters. Despite the disturbances, the designed control system assures tracking of the setpoints of flight path angle and heading by actively changing the thrust lever position (\(\delta\)T\({}_{\text{L}}\) and \(\delta\)T\({}_{\text{R}}\) signals). However, the settling time taken to reach the glide path direction was extended in connection with roll angle \(\phi\) fluctuations between the 180 th and 270 th second of the simulation. The short approach distance, combined with the lateral gusts, resulted in the landing aircraft being within the lateral boundaries of the runway just before touchdown. Nevertheless, the system enabled the machine to land safely with a final flight path angle close to the value obtained during the attempt made in windless conditions. Figure 8: Control parameters during landing attempts: (**a**) in windless conditions; (**b**) in crosswinds of 14 kts. Figure 9: Glide path altitude tracking: (**a**) in windless conditions; (**b**) in crosswinds of 14 kts. As shown in Figure 9b, even in the presence of gusts, the control system maintained the set glide path.