Intercepting an Active Leg

The instruction that you provided is something that I get regularly.  When you activate the leg, the magenta line becomes your desired navigation track (DTK) and you have some type of cross track deviation since you are left or right of course by some amount.  The question becomes, at what intercept angle does the IFD calculate to intercept the active leg.  I don't know the answer to that.  However, in practice, I put the autopilot in heading mode since ATC gave you a specific heading to fly (in this case 360), and then arm the GPSS mode (this worked on my 55X with built in GPSS).  In an autopilot where GPSS is not integrated, and you have a GPSS module, or in your case GPSS from the Aspen,  I don't know what you can do.  An alternative, is to use heading mode, and arm the NAV mode on the autopilot (all but the basic STEC autopilots can do this).  This will fly the proper intercept course instructed by ATC, and will automatically turn on course once the active leg is intercepted (by switching to NAV mode, or GPSS mode in a 55X).

I have a simple autopilot, an STEC-30 with GPSS and altitude hold. There's a switch on my panel that selects between HDG and GPS. Whenever I'm flying heading assigned by ATC I stay in HDG mode, and dial the appropriate heading into the DG of my plane. I stay with that until I want to continue following my IFD540 instructions. I'm pretty much with Bob, if you want to fly a heading, stay in HDG mode.