Definition
An error in radio navigation signal reception caused by the physical characteristics of the ground around the receiving antenna and the surrounding terrain. Hills, mountains, buildings, vegetation, soil conductivity, and reflective surfaces near the antenna can distort, reflect, or weaken the incoming signal, producing inaccurate bearing or position information.
Plain English
A navigation signal error caused by the land and objects around the antenna. Hills, buildings, and the type of ground can bend or reflect the radio waves, so the instrument shows a slightly wrong reading.
Context Anchor
Seen in instrument flying when learning why ground-based radio navigation signals can have small errors even when the aircraft equipment is working properly.
Derivation
‘Site’ comes from the Latin situs, meaning ‘position’ or ‘location’ — here it refers to the specific spot where the antenna sits. ‘Terrain’ comes from the Latin terra, meaning ‘land.’ Together they describe errors caused by where the antenna is placed and what kind of land surrounds it.
Why Pilots Care
Bearings and positions from ground-based navaids are not perfectly reliable when terrain or local conditions interfere. Knowing this helps pilots cross-check navigation information and stay alert to small inaccuracies, especially in mountainous areas or near large structures.
Grounding Statement
A signal that travels straight from the station can be more accurate than one that has been weakened or reflected by the ground around the station.
Intuition Check
Do not read “site and terrain error” as a pilot’s mistake in choosing a site or avoiding terrain. Here it means an error in the radio navigation indication caused by the transmitter’s surroundings and the land between the station and the aircraft.
Example Sentence 1
The instructor explained that site and terrain error can cause the ADF needle to give an inaccurate bearing when the station is surrounded by hills.
Example Sentence 2
Site and terrain errors become noticeable when the navigation aid is located near reflective surfaces.