Final answer:
The best action when 400' high at a high key during a forced approach is to enter a downwind leg and descend to rectify the excess altitude, while considering the aircraft's performance and environmental conditions.
Step-by-step explanation:
In the scenario where you are 400' high at your high key during a forced approach, the best course of action would typically be to enter a downwind leg and descend to lose the excess altitude. This downwind leg would allow you to adjust your flight path without drastically changing your location in relation to the landing site. However, it's important to incorporate the specifics of your plane's performance and the current environmental conditions when making this decision. If you find yourself in this situation, it's crucial to maintain safety and control of the aircraft while also efficiently correcting your altitude.