MtnFly Simulations have been developing a freeware Learjet-25A and have recently released a substantial progress update, outlining what has to be done, what is complete and even showcasing a full flight of the aircraft on their youtube channel. 

Their update log outlining what has been done is as follows: 

- NAV and COM radios are fully functional and will now work with the Garmin GPS even though there is no concept of a true standby frequency in the early model 35's radios.

- The yaw damper has been modelled and is now functioning.

- The three AC to DC power inverters are now modelled and functioning.

- The FC-200 autopilot is now working as expected.

- Improvements have been made to the side audio panels.

- All four batteries are now connected to their respective power busses and function 

- The captain's flight instruments are close to being fully functional.

- The emergency brake lever has been modelled and now functions.

- The cabin temperature indicator will now display a "cold-soaked" temperature on start-up. It will react to the user's set temperature setting once the engines are running and the passenger air conditioning system is turned on.

- Improvements have been made to tying electrical circuits to their respective circuit breakers.

- The RCA WXD weather radar has been modelled for those that prefer to fly "old school" without any GPS.

- Panel lighting has been added.

- Exterior Lighting has been added.

- There have been many improvements to emissive lighting throughout the aircraft.

- The wing to fuselage fairing has been added.

- There have been numerous modelling updates.

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At Threshold we will keep you updated while this project progresses.