## 3 Research Environment and Plan of Experiment
### Simulation Assumptions  
The simulations were conducted under the following assumptions:  
* Aircraft weight: 65,000 kg,
* Automatic flight with a layer of atmospheric gusts
* Three flight phases: descent, level flight and climb
* Simulation performed by a pilot holding a current type rating for the B737.  
Automatic simulated flights were carried out using the following autopilot and autothrottle modes:  
* LVL CHG (Level Change). This mode coordinates pitch and thrust commands to perform automatic climbs and descents to preselected altitudes at specified airspeeds. During descent, the autothrottle mode annunciates RETARD, followed by ARM, and then maintains the idle thrust. During the climb, the autothrottle mode annunciates N1 for climb and holds limit thrust for CLB from FMC. In both cases, the Autopilot Flight Director System (AFDS) holds the selected airspeed [45]. The rate of climb is a resulting parameter. This mode allows for the assumption of approximately constant thrust during simulation (the VS--Vertical Speed mode maintains a constant vertical speed, adjusting thrust and pitch to hold the selected IAS and vertical speed VVI).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Source** & **Symbol—Unit** &
\begin{tabular}{c} **Sampling** \\ **Frequency** \\ \end{tabular} \\ \hline Time & Simulation time & t [s] & 12.5 Hz \\ \hline Altitude & Cockpit indicator & ALT [m] & 12.5 Hz \\ \hline Indicated Air Speed & Cockpit indicator & IAS [m/s & 12.5 Hz \\ \hline True Air Speed & Cockpit indicator & TAS [m/s] & 12.5 Hz \\ \hline Ground Speed & Flight model position & GS\_x [m/s] & 12.5 Hz \\ \hline Vertical Speed & Cockpit indicator & VVI [m/s] & 12.5 Hz \\ \hline Wind speed x (OGL) & Simulation weather & Wind\_x [m/s] & 12.5 Hz \\ \hline Wind speed y (OGL) & Simulation weather & Wind\_y [m/s] & 12.5 Hz \\ \hline Wind speed z (OGL) & Simulation weather & Wind\_z [m/s] & 12.5 Hz \\ \hline Pitch rate & Flight model position & Q [deg/s] & 12.5 Hz \\ \hline Pitch angular acceleration & Flight model position & Q\_dot [deg/s\({}^{2}\)] & 12.5 Hz \\ \hline Horizontal Stabilizer & \multirow{2}{*}{Flight model controls} & HS\_elev [deg] & 12.5 Hz \\ elevator deflection & & & \\ \hline Side acceleration & Flight model position & G\_side [m/s\({}^{2}\)] & 12.5 Hz \\ \hline Magnetic Heading & Flight model position & HDG [deg] & 12.5 Hz \\ \hline Magnetic Track & Flight model position & TRK [deg] & 12.5 Hz \\ \hline Theta angle & Flight model position & Theta [deg] & 12.5 Hz \\ \hline Angle of attack & Flight model position & Alpha [deg] & 12.5 Hz \\ \hline Flight path angle & Flight model position & Flightpath [deg] & 12.5 Hz \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters recorded in the X-Plane environment for the purposes of testing gust estimation algorithms.  
* ALT HLD (Altitude Hold). In this mode, the autopilot commands pitch to hold the uncorrected barometric altitude at which the switch was pressed or MCP (Mode Control Panel) selected altitude after climb or descent. The autothrottle system holds the selected speed indicated in the IAS/MACH display on the MCP by adjusting the throttle control and thrust accordingly.
* HDG SEL (Heading Select). This mode commands roll to turn to and maintain the heading set on the MCP HEADING display. The maximum bank angle limit is limited by the bank angle selector [45].  
The amplitudes of simulated gusts used in the tests were determined (taking into account the limitations of the simulation environment) based on empirical data and documented reports [46; 47]. Peak values of headwind changes or downdrafts may slightly exceed the design gust envelopes defined in CS-25 and FAR 25 [48; 49], but they remain valid for simulating extreme transient events. The gust amplitudes used in the simulations are considered physically plausible and appropriate for modeling extreme yet credible scenarios--particularly those associated with terrain-induced gusts, thunderstorms, or microburst conditions.