Definition
In the primary/support instrument method of attitude instrument flying, 'primary for power' identifies the instrument that gives the most direct, immediate indication of whether the engine power setting is correct for the flight condition being maintained. Which instrument is primary for power depends on the maneuver: in straight-and-level cruise it is the airspeed indicator; in a constant-airspeed climb or descent it is the tachometer or manifold pressure gauge; in a constant-rate climb or descent at a fixed airspeed it is also the power instrument (tachometer or manifold pressure gauge).
Plain English
It is the one instrument the pilot watches most closely to confirm the power setting is right for what the airplane is doing at that moment. Other instruments are checked too, but this one is the main reference for power.
Context Anchor
Seen in instrument flying discussions and tables that show which instruments are used first for pitch, bank, and power during level flight, climbs, descents, and turns.
Derivation
Primary comes from a Latin word meaning “first.” In this phrase, it means first in use or importance for that part of flying. Power refers to the engine output being used to fly the airplane.
Why Pilots Care
Selecting the correct primary instrument for power keeps the aircraft at the intended speed and performance without over-controlling the throttle or creating unnecessary workload.
Intuition Check
Primary does not mean the only instrument you may look at. It means the first and most important instrument for checking power in that specific maneuver.
Example Sentence 1
In level cruise, the airspeed indicator is primary for power, so the pilot uses it to confirm the throttle setting is producing the target cruise speed.
Example Sentence 2
While climbing, the pilot treats the manifold pressure gauge as primary for power and sets it to the value that produces the planned rate of climb.