## 3 Air Data System Description and Functions
### ADS Functionalities  
The ADS can directly measure (1) local static pressure, (2) local dynamic pressure, and (3) local total air temperature. In contrast, the ADS can estimate (without using any dedicated physical vane/probe) (1) the freestream angle of attack and (2) the freestream angle of sideslip. From these five main air data (three measured and two estimated), the air data system can calculate all the air data necessary to be compliant with [5]. Table 2 collects the main air data functionalities of the ADS and possible effects from the total loss of the single function. Among all data, airspeeds (e.g., CAS and TAS), pressure altitude, and vertical speed are the most relevant, whereas the measure of the angle of attack is typically used for stall prevention [43] or flight control laws. In fact, the AoA accuracy requirements are typically derived from flight mechanics, control, and/or manoeuvrability considerations. As far as AoS is concerned, the standard AS8002A [5] does not prescribe any requirements. The AoS measure and accuracy requirements are only derived from flight mechanics, control, and/or manoeuvrability considerations.  
It is worth highlighting that local air temperature measures are calibrated using airspeed or Mach number information. Therefore, any loss in speed indications causes a degradation in the measurement of the freestream air temperature.  
Table 3 provides the dependency between air data functionalities and the ADS main parts.  
As far as degraded ADFs are concerned, they are not considered in this work because they would require a dedicated sensitivity analysis. In other words, even though the loss of a TAT probe (or its main related function ADF2) affects the synthetic estimation of AoA and AoS, data degradation will be considered within the acceptance limits. The loss of  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Function ID** & **Function Description** & **Loss Effects** \\ \hline ADS1.1 & Measure of static pressure & Loss of Pressure Altitude, Vertical Speed, IAS, CAS, EAS, TAS, Mach Number, AoA, and AoS; Degraded measure of Air Temperature \\ \hline ADS1.2 & Measure of dynamic pressure & Loss of IAS, CAS, EAS, TAS, Mach Number, AoA, and AoS; \\  & & Degraded measure of Air Temperature \\ \hline ADS2 & Measure of air temperature & Loss of TAS and Air Temperature; Degraded estimation of AoA and AoS \\ \hline ADS3 & Estimation of AoA & Loss of AoA \\ \hline ADS4 & Estimation of AoS & Loss of AoS \\ \hline \hline \end{tabular}
\end{table}
Table 2: ADS function requirements and loss effects.  
\begin{table}
\begin{tabular}{l l c c c c c} \hline \hline \multicolumn{3}{c}{**Air Data System**} & \multicolumn{6}{c}{**Functional Requirement Allocation**} \\ \hline
**Part** & **Sub-Parts** & **ADS1.1** & **ADS1.2** & **ADS2** & **ADS3** & **ADS4** \\ \hline  & Tube, ducts and struct & X & X & x & X & X \\ Pitot probe & Heater & X & X & x & X & X \\ \hline  & Probe & & & & X & x \\ TAT probe & Heater & & & X & x & x \\  & Sensing element & & & X & x & x \\ \hline ADC & Board & X & X & X & X & X \\ Abs. press. transl. & X & & x & & \\ Diff. press. transl. & & X & x & X & X \\ \hline FCC data & & & & & & X \\ (input to ADS) & N/A & & & & & X \\ \hline \hline \end{tabular}
\end{table}
Table 3: ADS decomposition and functional requirement allocation to main parts. “X” represents a full loss, whereas “x” is a degraded function.  
ADF1 (pressure measurements) will affect the temperature calibration. Even in this case, the degradation will be considered acceptable.