Definition
The segments of a flight during which the workload is highest and the margin for error is lowest, specifically taxi, takeoff, landing, and all flight operations conducted below 10,000 feet (except cruise flight). During these segments, flight crews are required by the Sterile Flight Deck Rule to limit their activity to duties essential to the safe operation of the aircraft.
Plain English
The parts of a flight where the most can go wrong and the crew needs to focus completely on flying. This covers ground movement, takeoff, landing, and any flying below 10,000 feet other than steady cruise.
Context Anchor
Seen in sterile flight deck or sterile cockpit discussions, especially when deciding what conversation or activity is allowed during taxi, takeoff, landing, and low-altitude flight.
Derivation
"Critical" comes from the Greek kritikos, meaning "able to judge" or "decisive." In aviation it carries the sense of "a moment where the outcome is decided" — these are the phases where small errors become big problems quickly.
Why Pilots Care
Distractions during these phases are a leading factor in runway incursions, altitude deviations, and approach-and-landing accidents; the sterile rule exists to eliminate them.
Intuition Check
Do not read critical phases of flight as just any moment that feels important. In the sterile flight deck rule, it has a specific meaning tied to taxi, takeoff, landing, and most flight below 10,000 feet.
Example Sentence 1
During critical phases of flight, the crew kept all conversation limited to checklist items and aircraft control.
Example Sentence 2
Below 10,000 feet the first officer kept all conversation to flight-related items only, recognizing they were still in a critical phase of flight.