Definition
A condition detected by a Ground Proximity Warning System (GPWS) or Terrain Awareness and Warning System (TAWS) in which the aircraft is approaching the terrain below it too quickly for safe continuation, based on the rate at which the radio altimeter reading is decreasing. When the closure rate exceeds preset thresholds for the aircraft's altitude and configuration, the system issues an aural and visual warning so the crew can take immediate corrective action.
Plain English
The ground is coming up at you faster than it should be, and the warning system is telling you to do something about it now.
Context Anchor
Seen in terrain alerting system discussions, especially warnings that protect against controlled flight into terrain.
Derivation
Closure here means the rate at which two things are coming together — in this case, the aircraft and the ground. Excessive simply means more than the system considers safe for the current phase of flight. The phrase describes the gap closing too fast.
Why Pilots Care
Triggers an immediate terrain warning to prevent controlled flight into terrain.
Analogy
It is like driving toward a wall: the danger is not just how far away the wall is, but how fast that distance is disappearing.
Grounding Statement
Picture an aircraft flying toward rising ground; even if the aircraft is level, the ground can be coming up toward it too quickly.
Intuition Check
Do not read closure as closing something shut. Here, closure means the aircraft and terrain are getting closer together, and excessive means that is happening faster than the system considers safe.
Example Sentence 1
While descending through an area of rising terrain at night, the crew received an excessive closure rate warning and immediately initiated a climb.
Example Sentence 2
An excessive closure rate alert requires immediate climb to restore safe separation from terrain.