I am using a retrofit I found on the main ISG website, the analog panel with the Smiths FMS.
I perform departures by hand, and once I passed through 6000... tried having the aircraft fly by the FMS.
I turned on the autopilot, set my altitude to desired cruising alt, set speed, then turned on HDG hold and ALT hold.
After engaging the LNAV and VNAV buttons, they seemed to work... but over time I noticed LNAV was not correctly holding the heading.
I would turn to a heading to intercept the course again, and once intercepted I engaged LNAV, but it would just keep ticking the heading bug past the intended heading.
I am using the freeware release of the RFP747, with this retrofit: Analog version /w Smiths FMS, and ND & ND popup. By SIMU_3G7
http://isgsim.com/retrofits/rfp_742_smi ... trofit.zip