Definition
In instrument cross-check theory, the instruments that most directly show performance toward the pilot's immediate objective during a given maneuver. Which instruments are 'important' changes with the phase of flight: in straight-and-level flight, the heading indicator, altimeter, and attitude indicator are typically most important; in a level turn, the altimeter and attitude indicator take priority; in a climb or descent, the vertical speed indicator and airspeed indicator become more important.
Plain English
The instruments you should look at most often during a particular maneuver because they tell you most directly whether you are doing what you intend to do.
Context Anchor
Seen in instrument cross-check discussions, where the pilot must decide which instruments need more attention during a climb, turn, descent, approach, or correction.
Derivation
Important comes from a Latin idea meaning “to carry weight.” Instrument comes from a Latin word meaning “tool” or “equipment.” Together, the phrase points to the aircraft tools that carry the most weight for the task at hand.
Why Pilots Care
Focusing on the right instruments first keeps the aircraft under control and prevents spatial disorientation or altitude deviations.
Intuition Check
Do not read “important instruments” as a fixed list of the same gauges every time. In this context, it means the instruments that are most important for what the aircraft is doing right now.
Example Sentence 1
During a straight climb, the airspeed indicator and attitude indicator become the important instruments, so the pilot scans them more frequently.
Example Sentence 2
When established in straight-and-level flight the pilot returned attention to the important instruments to confirm altitude and heading were stable.