What is the primary restriction on thrust reversers during the preflight check?

The primary restriction on thrust reversers during the preflight check is that they must not exceed Reverse Idle. This means that during the check, the operation of the thrust reversers should be verified without advancing the thrust levers beyond the Reverse Idle position. Maintaining the thrust reversers in this position is essential because exceeding this limit could cause structural or operational issues, particularly on the ground during preflight checks.

This practice ensures that the thrust reversers are functioning correctly and can transition to Reverse Idle, which confirms their readiness for use during landing. It also prevents any excessive thrust that could potentially affect the aircraft's stability or safety during the preflight assessment. Prioritizing the Reverse Idle position during the check helps to ensure smooth and safe operation of the aircraft upon landing when full reversing is required.