Which of the following maneuvers is prohibited for the T-54A?

Intentional spins are prohibited for the T-54A due to the inherent risks and potential for loss of control during such maneuvers. Spins can result in significant altitude loss and may lead to dangerous situations if not executed with proper training and precautions. The T-54A, designed primarily as a combat vehicle, is not equipped for aerobatic flight, and intentional spins would not only violate operational protocols but also endanger the crew and equipment.

In contrast, the other options, while they may have specific operational guidelines, do not carry the same outright prohibition. For example, landing below 600 feet per minute (FPM) could be managed with appropriate technique and conditions, as could emergency descents when necessary. Stalls at high altitude, while certainly not ideal, can be a part of training and recovery procedures if managed correctly within a safe operational framework.