Excessive bank angles at high altitudes are hazardous because:

Excessive bank angles at high altitudes can indeed present multiple hazards, which is why the correct response considers all the provided factors.

When an aircraft banks excessively, it increases the load factor on the wings. At high altitudes, this elevated load factor can lead to a greater risk of stalling because the aircraft may exceed its critical angle of attack even while airspeed is relatively high. This is due to changes in lift dynamics that occur as the angle of bank increases. Furthermore, the increase in angle of attack that comes with higher bank angles can create additional drag, which can further push the aircraft closer to stall conditions.

At high altitudes, engines also produce less thrust due to a decrease in air density. This reduced engine performance can compound the situation as the aircraft may struggle to maintain altitude, especially when combined with the increased drag that comes with high bank angles.

Lastly, operating close to buffet boundaries becomes a critical issue with excessive banking at high altitudes. As the airplane approaches the limit of its aerodynamics, it may experience buffet before reaching stall conditions. This is important because the threshold at which buffet begins often decreases with increased load factor, meaning that pilots need to give more attention to load management at these altitudes.

Recognizing all