What protection is lost if the EPR mode fails?

When the EPR (Engine Pressure Ratio) mode fails, alpha floor protection is compromised. Alpha floor protection is a safety feature that prevents the aircraft from stalling by automatically applying maximum thrust when the aircraft’s angle of attack reaches a critical threshold. This function relies on reliable data input, including the EPR, to determine the appropriate thrust settings needed to maintain safe flight characteristics.

In the absence of EPR mode functionality, the system cannot accurately gauge engine performance relative to atmospheric conditions, resulting in a loss of this critical protective mechanism. Consequently, the aircraft may not automatically respond to situations where the angle of attack is excessive, increasing the risk of a stall if the pilot does not intervene promptly.

The other types of protections, such as high angle of attack protection, roll protection, and pitch protection, are associated with different systems and controls in the aircraft's flight envelope management. While they are essential for safe operation, their functionality does not directly hinge on the EPR mode, which is why those protections remain unaffected in the event of an EPR mode failure.