Definition
Movable panels in a turbofan engine's thrust reverser system that, when deployed, swing into the fan or exhaust airflow path and redirect that airflow forward to produce reverse thrust during the landing roll.
Plain English
Doors inside the engine that close across the airflow when the pilot selects reverse thrust, so the air is pushed forward instead of straight out the back. That forward push slows the airplane down.
Context Anchor
Seen in descriptions of thrust reverser operation, especially on jet airplanes that redirect engine airflow after touchdown.
Derivation
Called blocking doors because they physically block the normal rearward path of the engine's airflow, forcing it to exit through side openings angled forward.
Why Pilots Care
Proper deployment ensures effective deceleration and reduces brake and tire wear on landing.
Analogy
They work a little like placing a board in a stream of water so the water cannot keep going straight and must turn another way.
Intuition Check
Do not think of blocking doors as cabin or cargo doors. Here, they are internal engine panels that block and redirect airflow.
Example Sentence 1
When the pilot selected reverse thrust after touchdown, the blocking doors deployed and the airplane decelerated firmly.
Example Sentence 2
During preflight the crew verified that the blocking doors moved freely and seated correctly.