What is the limit for the preflight check of the thrust reversers?

The limit for the preflight check of the thrust reversers is that they must not exceed Reverse Idle. This is crucial because during the preflight checks, the primary goal is to ensure that the thrust reversers are functioning correctly without applying excessive thrust that could put the system or aircraft at risk. Ensuring that the thrust reversers only operate to Reverse Idle allows for safe testing while not risking any unintended thrust scenarios that could impact preflight safety protocols.

Choosing Reverse Idle ensures that the checks assess the reversers' operational integrity without introducing dynamic thrust that could lead to potential hazards, such as generating unwanted forces on the airframe or affecting the aircraft's ground handling characteristics.