What is the minimum altitude the autopilot may be used during a glidepath angle of 3.5° or less?

The minimum altitude at which the autopilot can be used during a glidepath angle of 3.5° or less is indeed 80 feet Above Ground Level (AGL). This altitude is established based on regulatory standards and safety practices that encompass the operational limits of autopilot systems. The primary reason for this minimum altitude is to ensure that the autopilot can effectively manage the aircraft's performance during its final approach phase without compromising safety or control stability.

Using the autopilot at this altitude allows for a smoother transition as the aircraft descends on approach while still providing sufficient time and altitude for the pilot to take manual control if necessary. It balances the benefits of automation with the need for pilot oversight during critical phases of flight, particularly as the aircraft approaches the runway.

In contrast, the other altitudes listed are either below the operational limits set for autopilot use or do not comply with safety standards required for a safe landing approach under those glidepath conditions. Therefore, the selection of 80 feet AGL is reflective of a well-considered compromise between automation and pilot capability during a glidepath descent scenario.