@dadgametime
No doubt (qualified guess) F28 used the same INS system as Fokker F50. (licensed tech course on F50).
Calibrating updating INS during flight, the system preferred at least 2 DME for triangular calculation, secondary VOR direction. Least preferred was GPS. Great to pinpoint a place on earth but not altitude. The slant range is better with DME/VOR calculation for altitude.
For me - I keep the F28 as is - and wait for F70 and F100.