What is the primary concern when operating at extreme altitudes for turbojet engines?

When operating at extreme altitudes, the primary concern for turbojet engines is low combustion chamber pressures. As altitude increases, the atmospheric pressure decreases, leading to lower air density. This reduced air density can affect the engine's ability to intake sufficient air for combustion, which in turn can lower the pressures within the combustion chamber. Maintaining optimal combustion chamber pressure is crucial for ensuring efficient engine performance and avoiding potential issues related to combustion stability.

At high altitudes, the turbojet engine's operational efficiency can be significantly impacted due to these changes in pressure, which can lead to incomplete combustion or instability within the engine. This situation requires careful monitoring and management to ensure that the engine operates within its designed parameters and remains safe and efficient.