Which of the following is NOT a performance instrument?

The fuel flow gauge is classified as a measurement instrument rather than a performance instrument. Performance instruments are typically those that provide real-time information about the aircraft's performance capabilities, such as the rate of turn, altitude changes, and flight attitude. The fuel flow gauge, while important for managing fuel consumption and ensuring sufficient fuel for flight, does not directly measure or indicate the aircraft's performance, but rather informs the pilot about fuel usage versus what is available.

In contrast, the MSI (Multi-Function Display), heading indicator, and turn and slip inclinometer are all focused on aspects of aircraft operation and performance. The MSI integrates various data for situational awareness, the heading indicator provides critical information on the aircraft's orientation, and the turn and slip inclinometer indicates the rate of turn and helps maintain coordinated flight. These instruments are essential for making informed decisions about the aircraft's performance during flight, aligning them with the characteristics of performance instrumentation.