Safety Analysis of a Certifiable Air Data System Based on Synthetic Sensors for Flow Angle Estimation

Abstract

This work deals with the safety analysis of an air data system (ADS) partially based on synthetic sensors. The ADS is designed for the small aircraft transportation (SAT) community and is suitable for future unmanned aerial vehicles and urban air mobility applications. The ADS’s main innovation is based on estimation of the flow angles (angle-of-attack and angle-of-sideslip) using synthetic sensors instead of classical vanes (or sensors), whereas pressure and temperature are directly measured with Pitot and temperature probes. As the air data system is a safety-critical system, safety analyses are performed and the results are compared with the safety objectives required by the aircraft integrator. The present paper introduces the common aeronautical procedures for system safety assessment applied to a safety critical system partially based on synthetic sensors. The mean time between failures of ADS’s sub-parts are estimated on a statistical basis in order to evaluate the failure rate of the ADS’s functions. The proposed safety analysis is also useful in identifying the most critical air data system parts and sub-parts. Possible technological gaps to be filled to achieve the airworthiness safety objectives with nonredundant architectures are also identified.

Geodetic Altitude from Barometer and Weather Data for GNSS Integrity Monitoring in Aviation

“…The airborne side, based on work by Lerro & Battipede (2021), may be broken down to the hardware (HW) ADS parts, which are involved in the execution and analog-to-digital conversion of the barometric pressure measurements. Lerro & Battipede (2021) focused on an ADS designed for use cases in the small aircraft transportation (SAT) sector.…”

“…The airborne side, based on work by Lerro & Battipede (2021), may be broken down to the hardware (HW) ADS parts, which are involved in the execution and analog-to-digital conversion of the barometric pressure measurements. Lerro & Battipede (2021) focused on an ADS designed for use cases in the small aircraft transportation (SAT) sector. The ADS is decomposed down to the probe, piping, and heater of the Pitot tube and down to the pressure transducer and the two HW boards (one being redundant) that are part of the ADC.…”

“…Adopting this airborne fault rate for airplanes in the transport category, which is classified in accordance with European Union Aviation Safety Agency (EASA) CS-25 or Federal Aviation Administration 14 CFR Part 25, can be considered a conservative approach. In fact, it is expected that EASA CS-25-classified airplanes are provided with ADSs of a higher grade with respect to EASA CS-23-classified airplanes, such as SAT aircraft (Di Vito et al, 2021;Lerro & Battipede, 2021;Piwek & Wiśniowski, 2016).…”

GNSS Autonomous Integrity Monitoring with Barometric Pressure Measurements and Weather Data

“…Based on (Lerro and Battipede, 2021), the airborne side may be decomposed down to the hardware Air Data System (ADS) parts which are involved in the performance and analog-to-digital conversion of the static air pressure measurements. This concept focuses on an ADS designed for small aircraft transportation (SAT) use cases.…”

“…Adopting this airborne FR for airplanes in the transport category, that is classified according to EASA CS-25 or FAA's 14 CFR Part 25, can be considered a conservative approach, since the ADS analyzed in (Lerro and Battipede, 2021) is designed for SAT, which belongs to EASA CS-23 (Lerro and Battipede, 2021;Piwek and Wiśniowski, 2016;Di Vito and Torrano, 2017). Indeed, it is expected that EASA CS-25 classified airplanes are equipped with ADSs of a higher grade with respect to the EASA CS-23 classified ones.…”