A red diagonal on AFTO 781A indicates what about the equipment?

A red diagonal on an AFTO 781A indicates that there is a discrepancy with the equipment. This marking signals that something is not functioning as expected or that there is an issue that needs attention. The purpose of the red diagonal is to visually alert personnel about the problem, prompting further investigation or corrective action. This is crucial for maintaining the safety and operational readiness of the equipment, as it helps ensure that issues are addressed quickly.