Which of the following is NOT a component of the aircraft's pneumatic system?

The correct answer is the fuel flow meter, as it is not a component of the aircraft's pneumatic system. The pneumatic system primarily deals with the management and utilization of compressed air or gases to operate various aircraft functions, including the operation of components that require pneumatic pressure for functioning.

The bleed air valve regulates air that is bled from engines or auxiliary power units for use in the pneumatic system, while the pneumatic pressure gauge measures the pressure within that system, providing vital information for monitoring and safety. The pressure relief valve serves as a safety component, ensuring excess pressure is vented to prevent system damage. All these components are integral to the pneumatic system, highlighting that the fuel flow meter serves a different function related to monitoring fuel rather than operating pneumatic functions.