What is the transition layer in aviation?

The transition layer in aviation refers to the specific zone between the transition altitude and the transition level. This layer is crucial for maintaining separation between aircraft flying at altitudes using different reference systems. The transition altitude is the height where pilots switch from altitude readings (using the local altimeter setting) to flight levels (which are based on a standard pressure setting of 29.92 inHg). Conversely, the transition level is the lowest flight level available for use in the region of transition, which is above the transition altitude.

By maintaining a defined transition layer, it ensures that there is a safe buffer between aircraft operating in altitude mode and those in flight level mode, thereby preventing any potential collisions or confusion about aircraft altitude versus flight level during ascent and descent. This layer is particularly important in busy airspace, where multiple aircraft may be changing altitudes and levels frequently.

The other answers focus on different aspects of aviation but do not accurately define the transition layer. For instance, the region above the transition altitude is not the layer itself but rather the airspace where flight levels begin. Similarly, calibration of altimeters occurs at various points, but this process is not confined to the transition layer. Lastly, the space between sea level and 3,000 feet pertains more