At which altitude is a spin prohibited?

A spin is prohibited above 20,000 feet due to the increased risk associated with altitude during spin recovery and the physiological challenges that can arise at higher elevations. At elevations beyond this threshold, the aircraft may not have sufficient performance margins for recovery from such an aggravated flight maneuver. Also, the reduced air density at higher altitudes affects control effectiveness and response times, making recovery from spins increasingly difficult and dangerous. Hence, the limit of 20,000 feet is established to ensure pilot safety and optimal control of the aircraft during all flight conditions.