What should you not do with an engine that displays an "ENG STABILITY X" message on the WAP?

The best course of action when an "ENG STABILITY X" message appears on the WAP (Warning Annunciator Panel) is to avoid reversing the engine. The "ENG STABILITY X" alert indicates that there could be a problem with the engine's stability, which could lead to a potential failure or malfunction. Reversing the engine in this situation could exacerbate the problem or lead to an unsafe condition, especially during critical phases of flight or an emergency.

Instead, you would typically follow other procedures to ensure safety, which may include shutting down the engine or adjusting thrust levels as needed, depending on the specifics of the engine's failure indication. Checking fuel levels is often necessary, but it does not directly address the urgent concern posed by the instability warning.

In summary, the advisable approach when faced with this warning is to avoid engaging the engine in reverse, as this might compromise safety and control of the aircraft.