Definition
Ground features such as mountains, ridges, hills, cliffs, towers, antennas, or man-made obstacles that pose a collision risk to an aircraft if it descends below a safe altitude or strays from a protected flight path. In instrument approach design, hazardous terrain is the terrain and obstacles the published procedure is built to keep the aircraft clear of.
Plain English
Ground or objects sticking up from it that an airplane could hit if it gets too low or off course.
Context Anchor
Seen in instrument approach and RNAV/GPS approach discussions, especially where terrain affects how the approach must be flown.
Derivation
“Hazardous” comes from a word meaning risk or chance of danger. “Terrain” comes from a word meaning land or ground. Together, the phrase points to ground features that create a real risk to the airplane.
Why Pilots Care
Recognizing hazardous terrain prevents controlled flight into terrain accidents by ensuring proper altitude and routing decisions.
Grounding Statement
Picture an approach path near rising mountains: the terrain is not a problem while the airplane stays on the correct path and altitude, but it becomes hazardous if the airplane gets low or off course.
Intuition Check
Do not read “hazardous” as meaning the terrain is dangerous by itself. In aviation, it means the terrain becomes a hazard because of its height, location, and closeness to the aircraft’s path.
Example Sentence 1
The minimum descent altitude on this approach keeps us 500 feet above the hazardous terrain along the final approach course.
Example Sentence 2
Approach plates mark hazardous terrain so pilots can plan climbs or turns well before reaching the area.