Which of the following is NOT considered a control flight instrument?

A control flight instrument is essential for the pilot to operate the aircraft safely and efficiently by providing critical information about the aircraft's performance and flight state. The Electronic Attitude Director Indicator (EADI) serves as a primary control instrument, displaying essential flight data, especially regarding pitch and roll. Similarly, the N1 and N2 indicators, which represent engine speeds, are crucial for managing engine performance and ensuring optimal thrust during flight.

The Vertical Speed Indicator (VSI) provides important data regarding the aircraft's rate of climb or descent, helping pilots to maintain altitude or manage ascent or descent profiles effectively.

In contrast, Fuel Flow provides information related to fuel consumption rather than directly impacting the aircraft's flight control. Although important for overall operational efficiency and planning, it does not communicate immediate control-related data necessary for navigating or controlling the aircraft in flight. Thus, it is categorized differently from the other instruments listed, making it the correct answer to the question of which is NOT considered a control flight instrument.