Definition
An ICAO emergency phase declared when there is uncertainty about the safety of an aircraft and its occupants, typically because expected communications have not been received or the aircraft has failed to arrive at an expected time. It is the first and least severe of three escalating ICAO emergency phases, followed by the Alert Phase (Alerfa) and the Distress Phase (Detresfa).
Plain English
The first level of concern raised by air traffic services when an aircraft is overdue or hasn't checked in as expected, and no one is yet sure whether something is wrong.
Context Anchor
Seen in overdue-aircraft procedures, flight plan follow-up, air traffic control coordination, and search-and-rescue messages.
Derivation
Incerfa is a contraction of the French phrase 'phase d'incertitude,' meaning 'uncertainty phase.' ICAO uses French-derived contractions for its three emergency phases (Incerfa, Alerfa, Detresfa) so they can be transmitted clearly over radio without confusion with everyday English words.
Why Pilots Care
Declaration of INCERFA prompts ATC to begin checks and notify rescue services, starting a formal process that can locate an aircraft before a situation worsens.
Intuition Check
Uncertainty Phase does not mean the aircraft is confirmed to be in danger. It means the aircraft’s safety is unknown enough that authorities begin checking.
Example Sentence 1
When the aircraft failed to report at its estimated position fix and could not be raised on the radio, the controller declared Incerfa and began checking with adjacent sectors.
Example Sentence 2
The Uncertainty Phase, coded as INCERFA, is the first step in ICAO search and rescue before any alert or distress phase is considered.