What does the red radial marker on an engine instrument signify?

The red radial marker on an engine instrument signifies maximum limits for a specific parameter. In aviation, this marker is crucial for pilots and maintenance personnel as it visually communicates the upper threshold that should not be exceeded during operation. Exceeding this maximum limit could result in damage to the engine or affect its performance adversely. Therefore, the red radial marker serves as a clear and immediate warning to operators to keep the engine parameters within safe operational boundaries.

This understanding aligns with standard practices in aviation instrument readings, where color coding helps in quick identification of safe vs. hazardous operating conditions, ensuring that anyone operating or maintaining the aircraft remains aware of critical limits that should not be crossed.