What applications are powered by pneumatic systems in aircraft?

Pneumatic systems in aircraft are critical for various applications, particularly those requiring the use of compressed air. One of the primary applications is engine starting, where pneumatic power is utilized to initiate the combustion process in jet engines, ensuring a reliable start-up. Furthermore, air conditioning systems in aircraft utilize pneumatic systems to manage cabin temperature and air quality by controlling the flow of conditioned air.

This option encompasses significant aspects of aircraft operation, showcasing how pneumatic systems contribute to both engine functionality and passenger comfort. Both engine starting and air conditioning are fundamental operational components that rely on pneumatic systems, making this answer the most comprehensive and accurate choice among the options provided.