Definition
A systematic verification of flight, navigation, and engine instruments performed before takeoff to confirm that each instrument is powered, properly indicating, and functioning within acceptable tolerances. For IFR operations it includes checks of the attitude indicator, heading indicator, altimeter, vertical speed indicator, turn coordinator, magnetic compass, clock, pitot-static system indications, communication and navigation radios, transponder, and any required avionics or autopilot self-tests, performed at appropriate phases such as before engine start, after engine start, during taxi, and before takeoff.
Plain English
Before you fly, you check every instrument in the cockpit to make sure it is turned on, reading correctly, and working as it should.
Context Anchor
Encountered after engine start, before taxi or takeoff, when the pilot checks that the instruments are ready for flight.
Derivation
Preflight' simply means 'before flight.' The phrase emphasizes that these checks are completed on the ground, while problems can still be addressed safely.
Why Pilots Care
Catches instrument failures or misalignments on the ground so they do not become surprises or hazards once airborne, especially when outside visual references are lost.
Grounding Statement
With the engine running and the instruments powered, the pilot checks that the indications make sense before relying on them in the air.
Intuition Check
Do not assume “preflight” means only the walkaround before starting the engine. Here it means an instrument check completed before the flight begins, including checks made after engine start.
Example Sentence 1
During the preflight instrument check, she set the altimeter to the local setting and confirmed it read within 75 feet of the published field elevation.
Example Sentence 2
During the preflight instrument check the pilot turned the airplane to a known heading and verified the directional gyro matched the magnetic compass.