Definition
The lowest altitude, published on an ILS or other precision approach chart, at which an aircraft is permitted to intercept the glideslope inbound to the runway. Below this altitude, the glideslope signal is not guaranteed to be reliable, and obstacle clearance on the approach segment is not assured.
Plain English
The lowest height you are allowed to be at when you join the glideslope on an instrument approach. If you are lower than this, the approach is not protected and the glideslope signal may not be trustworthy.
Context Anchor
Seen on instrument approach charts and in ATC vectoring to the final approach course, especially when being assigned an altitude to maintain until established on the approach.
Derivation
“Glideslope” combines “glide,” meaning a smooth descent, with “slope,” meaning an inclined path. “Intercept” means to meet or join a path. Together, the phrase points to the altitude where the airplane may safely meet and begin following the descent path.
Why Pilots Care
Ensures the glideslope is captured at an altitude that preserves obstacle clearance and prevents an excessively steep or unstable descent.
Grounding Statement
Before you ride the glideslope down, you must be at or above the published altitude that keeps you safely clear of obstacles.
Intuition Check
“Minimum” does not mean “descend to this as soon as possible.” It means “do not intercept the glideslope below this altitude.”
Example Sentence 1
ATC vectored us onto final and assigned 2,000 feet, which matched the minimum glideslope intercept altitude shown on the chart.
Example Sentence 2
We reached the minimum glideslope intercept altitude and captured the glideslope without descending below the step-down fix.