Success comes in small steps... Finally, with the help of some enterprising souls here, I can see FSX from a remote client and read data... Like so: simconnect.AddToDataDefinition(DEFINITIONS.Struct1, "Autopilot Master", "Boolean", SIMCONNECT_DATATYPE.INT64, 0.0f, SimConnect.SIMCONNECT_UNUSED); Basically just add that to an existing STRUCT, get the data and everyone is happy. Let's say now that I want to change something, like toggle the A/P Master. The SDK comes with a few C# examples on how to read data, but none on how to write. Can anyone help?