## 3 Research Environment and Plan of Experiment
### Flight Plan and Its Realisation for Estimating Side Gusts  
To continue the development of the lateral gust estimation algorithm, a similar simulation methodology was employed. The aircraft was flown through a programmatically generated layer of gusts with a constant direction set at 90 degrees to the flight path. This configuration allowed for the simulation of ideal side gusts (with minimal frontal components and no vertical components). The minimally increasing frontal components resulted from the autopilot maintaining a given constant heading in the HDG SEL mode. As the drift angle was formed due to the increasing crosswind and increasingly stronger atmospheric gusts, small head-on gust components appeared. During the simulation, the aircraft descended from an altitude (ALT) of 12,000 ft (3660 m) to 6000 ft (1829 m) (6000 ft). The flight was fully automated using the autopilot in  
Figure 16: Registered ideal gusts measurements from the simulation weather section—climb phase; (**A**)—wind speed as a function of time, (**B**)—wind speed as a function of altitude. Figure 15: (**A**) Altitude, (**B**) IAS, and (**C**) VVI recorded during simulated flight—climb phase. LVL CHG mode. Basic flight parameters are shown in Figure 17. IAS fluctuations at the beginning and at the end of simulation in relation to the set speed of 250 kt (128.6 m/s) were caused by changes in flight phases: during the first 30 s of simulation--the transition from level flight to descent and from 280 s to 300 s--the transition from descent to level flight. The vertical speed during descent was the result of the MCP setting and logic of LVL CHG mode and was approximately 1380 ft/min (7 m/s). Minor fluctuations in the vertical speed were also caused by variable atmospheric side gusts and by changes in flight phases. At an altitude of 3660 m (12,000 ft), wind conditions were calm. After the descent commenced from this altitude, the crosswind (V\({}_{g}\)) began to increase. Between the 75 th and 240 th seconds of the recording, once the crosswind exceeded the speed of 4 m/s, sudden lateral gusts occurred reaching peak velocities of up to 23.5 m/s (Figure 18A,B). After passing 2600 m, side gusts started to decrease. From 2200 m to 1828.2 m (6000 ft), the crosswind gradually diminished until wind conditions became calm again. Subsequently, the test pilot performed simulated level flight through a crosswind layer containing lateral gusts. The autopilot and autothrottle systems were engaged in ALT HLD and HDG SEL modes with a constant altitude of 10,000 ft (3048 m) selected on the MCP. During simulation, only small fluctuations in the altitude, IAS, and vertical speed were recorded (Figure 19). On this basis, it can be concluded that side gusts had no significant impact on these three basic flight parameters. Figure 17: (**A**) Altitude, (**B**) IAS, and (**C**) VVI recorded during simulated flight—descent phase. Figure 18: Registered ideal gusts measurements from the simulation weather section—descent phase; (**A**)—wind speed as a function of time, (**B**)—wind speed as a function of altitude. As shown in Figure 20, side gusts generated by the simulator environment were highly dynamic, with gusts velocities increasing sharply from 6 m/s to 21 m/s over a short time interval. Similar to the level flight simulations involving head-on gusts, this flight was performed in crosswind layer without initial or final calm wind conditions. Minor frontal headwind components (below 2 m/s) occurred because of maintaining a constant heading in autopilot HDG SEL lateral mode. No vertical gusts components W\({}_{\text{g}}\) were observed during the simulation. The next simulation was conducted to evaluate the proposed method for estimating side gusts during the climb phase (Figures 21 and 22). The Boeing 737-800 was climbing from 600 ft (1828.2 m) to 14,000 ft (4267.2 m). At these specified altitudes, the wind was calm. Above an altitude of 2250 m, the crosswind exceeded 3 m/s, and side gusts with a maximum speed up to 21 m/s started to appear (Figure 22A,B).