Definition
The published or assigned altitudes a pilot is required to fly while operating under Instrument Flight Rules. These include minimum en route altitudes, minimum obstruction clearance altitudes, minimum vectoring altitudes, and altitudes assigned by ATC, all of which are designed to guarantee terrain and obstacle clearance, navigation signal reception, and safe vertical separation from other IFR traffic.
Plain English
These are the altitudes a pilot must fly when operating in the clouds or in low visibility under instrument rules. They are chosen so the aircraft stays clear of terrain, obstacles, and other traffic, even when the pilot cannot see outside.
Context Anchor
Seen in instrument flying, instrument charts, air traffic control clearances, and cold-weather altimeter correction guidance.
Derivation
IFR stands for Instrument Flight Rules, the body of regulations that governs flight by reference to instruments rather than by looking outside. An IFR altitude is therefore an altitude flown under those rules.
Why Pilots Care
Failure to adjust IFR altitudes in cold weather can result in terrain or obstacle clearance being lower than indicated, creating an immediate safety risk.
Grounding Statement
On a very cold day, an indicated IFR altitude can look safe while the aircraft is actually lower over the ground than the instrument suggests.
Intuition Check
IFR altitudes do not mean any altitude flown while the weather is bad. They mean assigned, published, or required altitudes used under instrument flight rules, often for separation or obstacle clearance.
Example Sentence 1
On a cold winter morning, the pilot applied a cold-temperature correction to the published IFR altitudes to make sure the aircraft truly cleared the mountains below.
Example Sentence 2
When temperatures drop well below standard, published IFR altitudes may no longer provide adequate terrain clearance without adjustment.