Definition
In the primary/supporting method of instrument scan, the primary instruments are those that provide the most direct and accurate indication of a specific aircraft performance parameter (pitch, bank, or power) for the maneuver being flown. The pilot maintains the desired value on each primary instrument while cross-checking the supporting instruments for trend information.
Plain English
For any given maneuver, certain instruments give you the clearest, most direct readout of how the aircraft is performing. Those are your primary instruments — the ones you hold steady on a target value while flying that maneuver.
Context Anchor
Seen in instrument scan and instrument interpretation discussions, especially when learning which gauges to rely on during straight-and-level flight, climbs, descents, and turns.
Derivation
From Latin primus, meaning 'first.' Here it means 'first in importance for this task' — the instrument you check first and hold to a target for that specific phase of flight. The primary instrument changes depending on what the airplane is doing.
Why Pilots Care
Selecting the correct primary instrument for each phase of flight gives precise control and prevents spatial disorientation when outside visual references are lost.
Grounding Statement
The primary instrument is the gauge that answers the most important question for what you are doing right now.
Intuition Check
Primary does not mean these instruments are always more important than all the others. It means they are the main references for the specific maneuver or control task at that moment.
Example Sentence 1
In straight-and-level flight, the altimeter is the primary instrument for pitch because it shows directly whether altitude is being held.
Example Sentence 2
Once established in a climb the airspeed indicator becomes the primary instrument for pitch control.