When must the caution strap be placed across the door opening on the ERJ 175?

The correct answer is that the caution strap must be placed across the door opening on the ERJ 175 when the door is open and unattended. This practice is critical for safety protocols, as it serves as a visual and physical barrier to alert personnel that the door is in an open position and should not be approached or utilized without proper oversight.

When the door is open and unattended, there is a risk that someone might unknowingly walk into the area, which could lead to accidents or injuries. The caution strap helps in preventing unauthorized access or unexpected actions around the door, ensuring that crew members are aware of the situation.

In contrast, placing the strap when the door is closed does not provide any safety benefit, as the risk is mitigated when the door is secured. Similarly, imposing the strap during pressurization does not directly correlate with safety as the door should not be open at that time. Lastly, using it only during a pre-flight check does not account for safety needs throughout the entire time the door is open, especially when it is unattended. Therefore, the correct timing for deploying the caution strap is indeed when the door is open and not under observation.