Definition
An evaluation of an instrument-rated pilot's ability to operate safely under instrument flight rules (IFR), conducted by an authorized examiner or instructor when the pilot has not met the recent instrument experience requirements within the preceding six calendar months plus a six-month grace period. The check covers the areas of operation and instrument tasks specified in the appropriate Airman Certification Standards or Practical Test Standards, and a satisfactory result restores the pilot's currency to act as pilot in command under IFR.
Plain English
A formal flight check that an instrument-rated pilot must pass to get back their ability to fly in the clouds when they have gone too long without enough recent instrument flying.
Context Anchor
You will see this term in discussions of instrument currency, flight reviews, recurrent training, and risk management for pilots returning to instrument flying after a gap.
Derivation
“Instrument” comes from a word meaning a tool or device; in aviation, it points to flying by the cockpit instruments instead of outside visual references. “Proficiency” comes from a root meaning to make progress or be capable, which fits the idea that the check is about demonstrated ability, not just time logged.
Why Pilots Care
Pilots who have not flown by instruments recently must pass one to remain legal to act as pilot in command under IFR.
Intuition Check
Do not read this as a check of the aircraft’s instruments. It is a check of the pilot’s ability to fly safely using the instruments.
Example Sentence 1
After two years of mostly VFR flying, the pilot scheduled an instrument proficiency check with a CFII before filing his next IFR flight plan.
Example Sentence 2
The instructor used the instrument proficiency check to evaluate the pilot's decision-making during simulated instrument failures.