Definition
A method of flying solely by reference to instruments in which, for each phase of flight, one instrument is designated the primary source for a given parameter (pitch, bank, power, or yaw) and the remaining instruments are used to support and cross-check that primary indication. The primary instrument is the one that gives the most direct and accurate reading of the desired performance once it has been established, while the supporting instruments help anticipate, confirm, and refine that performance.
Plain English
When flying without looking outside, you watch one main instrument for each thing you're trying to control, and use the others to back it up and cross-check.
Context Anchor
Used in instrument training when learning how to scan and interpret the flight instruments during climbs, descents, turns, and level flight.
Derivation
Primary' comes from the Latin primus, meaning 'first.' 'Supporting' means standing under or holding up. Together they describe a setup where one instrument is checked first for each task and the others stand behind it as backup.
Why Pilots Care
Provides a clear, repeatable way to maintain precise aircraft control in instrument meteorological conditions without relying on outside visual references.
Analogy
It is like driving while checking several mirrors and gauges, but knowing which one matters most for the task right now. You do not ignore the others; you use them to confirm the main information.
Intuition Check
Attitude does not mean the pilot’s mood here. It means the airplane’s position relative to the horizon. Primary does not mean the same instrument is always most important. The primary instrument can change depending on the maneuver and what the pilot is controlling.
Example Sentence 1
In straight-and-level flight, the altimeter is primary for pitch because it shows directly whether the desired altitude is being held.
Example Sentence 2
On the ILS approach the instructor had the student keep the attitude indicator as primary for pitch while cross-checking the altimeter and vertical speed indicator for altitude control.