How can a pilot determine if an aircraft is in trim?

A pilot can determine if an aircraft is in trim by feeling for necessary control forces to maintain flight. When an airplane is properly trimmed, it means that the control surfaces—especially the elevator—are set in such a way that minimal control input is required from the pilot to maintain a straight and level flight. The pilot should notice a neutral feeling in the control yoke or stick; if significant force is needed to hold the aircraft in a certain attitude, it indicates that the aircraft is out of trim.

Monitoring instrument readings and using autopilot controls do not provide a direct tactile feedback regarding the state of the aircraft’s trim. Instrument readings can indicate various flight parameters but do not specifically reflect whether the aircraft requires additional control force. Checking fuel levels, while important for overall flight management, has no direct correlation to the aircraft's trim status. Thus, the correct choice focuses on the physical feedback that a pilot actively feels from their controls to assess whether the aircraft is in trim.