Definition
The angular range used to define a Converging ILS Approach. Converging ILS approaches are authorized only when the angle between the final approach courses of the two intersecting ILS procedures is at least 15 degrees and no greater than 100 degrees. Below 15 degrees the courses are too close to provide adequate lateral separation between aircraft; above 100 degrees the geometry is no longer considered converging for procedural purposes.
Plain English
When two ILS approaches at the same airport cross each other, the angle where their final approach paths meet must be somewhere between 15 and 100 degrees for them to be used at the same time as a Converging ILS Approach.
Context Anchor
Seen in instrument approach procedure discussions for simultaneous ILS approaches to runways whose final approach paths point toward each other.
Why Pilots Care
Determines whether simultaneous operations are permitted and directly affects separation standards and missed approach routing.
Grounding Statement
Picture two runway approach paths drawn as lines on a map; the angle where those lines would meet must be between 15° and 100° for this criterion.
Intuition Check
15° and 100° are not compass headings here. They are angle limits between two final approach paths.
Example Sentence 1
The two runways' final approach courses intersect at 38 degrees, which falls within the 15° and 100° range required for a Converging ILS Approach.
Example Sentence 2
If the angle falls outside the 15° and 100° limits, ATC must use alternate separation methods instead of simultaneous converging approaches.