What visual change occurs to the scales on the Primary Engine Data Display (PEDD) during abnormal engine operations?

The correct answer highlights that during abnormal engine operations, the scales on the Primary Engine Data Display (PEDD) change color. This change in color serves as an important visual cue to the pilots, indicating that there is an issue that requires their attention. Color indicators help differentiate normal operating conditions from abnormal ones, enabling quick recognition and appropriate response to potential problems.

When the scales change color, it typically means that specific parameters are out of the acceptable range, signaling potential issues like over-temperature or excessive pressure, prompting immediate investigation. This visual alert system is critical for maintaining flight safety and operation.

In contrast, while some incorrect options suggest other forms of visual feedback, such as disappearing, enlarging, or blinking, these do not accurately reflect the standard design and function of the PEDD. The primary purpose is to ensure that any deviation from normal operations is clearly communicated to the pilots through a recognizable change, thus supporting effective decision-making in managing engine performance.