captjames wrote on May 17^th, 2016 at 5:10pm:

Good afternoon chaps! Apologies if this has been asked/ answered already. I just wondered if anyone knows a  way to "retrofit" the 737 to have an FMC to fly L/VNAV and proper flightplans? Thanks in advance, James

Hello James.

I have used the Flight 1 GTN 750 with success in the Tristar. The AP will follow the LNav.

As for VNav, well the 737-200 had only the CWS pitch, the IAS hold and the V/S mode (in later models).

The PDCS in the CS 737 gives some references to the pilot for climb rates, but no automated Vertical Speed. Later versions of the 737 featured early FMC. These had a link to the EPR and eventually the throttles in an Auto Throttle mode.  They went on to be the all singing FMC we see in the -600/800 etc.

So I would check out the F1 GTN 750. If you engage the VOR Nav and the GPS Switch on the glareshield, the aircraft should follow the GPS course from the GTN.

Cheers
David