I'm having some trouble getting the IMM DES (Immediate Descent) function to work in the Just Flight Fokker 70/100.

I'm using the latest release of the aircraft and have been following the procedures in the manual to the letter. However, whenever I try to activate IMM DES, the aircraft simply doesn't initiate a descent.

Could someone explain how this function is supposed to work? Are there any specific conditions that need to be met before IMM DES becomes available? For example, is there a certain distance or time before Top of Descent (TOD) when the function won't activate?

I'm not sure whether I'm missing something in the procedure or if this might be an issue with the aircraft.

Any help or clarification would be greatly appreciated!

Thanks in advance!