Analysis of Certification Requirements for Laser Doppler Anemometry in Large Aircraft

Kurzfassung

The Institute of Technical Physics at the Deutsches Zentrum für Luft- und Raumfahrt (German Aerospace Centre) (DLR) is developing a Laser Doppler Anemometer (LDA) capable of precisely measuring the airflow vector around an aircraft, which represents an alternative to Pitot-static systems and flow angle measurement vanes. These conventional systems are susceptible e.g. to icing and can provide unreliable air data while the LDA performs real-time uncertainty calculations on its measurements of True Air Speed (TAS), Angle of Attack (AoA), and Angle of Sideslip (AoS), supplying near-instantaneous information on the reliability of its data. Furthermore, the technology interacts only optically with the air. Flight tests confirmed the system’s feasibility and showed strong correlation between LDA measurements and reference data. Ongoing development efforts aim to further refine the technology, focusing on improving integration and performance while addressing lessons learned from the earlier campaigns. This thesis analysed the applicability of certification requirements for integrating LDA technology into large commercial aircraft regulated under CS-25. This was done by comparing conventional systems to the LDA technology, focusing on performance characteristics, novel risks and challenges as well as potential scenarios for integration. Certification Specification (CS) as well as industry standards (e.g. AS8002B, ARINC 738-3) applicable to state-of-the-art instruments were reviewed, and the gathered performance data was checked for its consistency. The comparison of the systems identified key advantages of the LDA including improved data integrity, aerodynamic benefits and simplified maintenance. As challenges for the introduction, asynchronous data rates and the need for adapted calibration procedures were identified. The study then proposed solutions to align the LDA with regulatory demands, such as statistical data rate compliance methods, revised accuracy requirements for TAS measurements and integration strategies for hybrid systems. Based on these analyses, the applicability of the CSs on the LDA was assessed. Additionally, potential adaptations to CS-25 were suggested to accommodate the novel measurement principles of the technology without compromising safety. The findings demonstrated that while LDA technology shows promise for enhancing aviation safety and efficiency, its adoption is complicated by regulation, prescribing conventional technology. While certification may be possible under a Special Condition (SC), more fundamental changes to the certification framework are suggested.