FMS STARs

[contractpilot 12]

Terry,Can you explain the difference between a FMS and RNAV STARs?Paul KuhnKPHX

[Guest staang]

Hi there Paul,I have to preface this by saying that while I have a commercial license I am not IFR certified. I only have about 4 hours IFR time logged so I speak with book knowledge not IFR flying experience.As far as flight simming goes I don't think there is a difference at all. None of the planes I work with differentiate between the two. They both do the same things as far as FS is concerned IE they are just a set of waypoints to follow.But for real world:The FMS STARs which I think you are referring to are designed using land based fixed radio navaids. I believe the system accuracy is bounded by 4 miles for 95% of the flight. The RNAV STARs are based on GPS coordinates. The system accuracy is bounded by 1 or 2 miles (type B or A) for 95% of the total flight time. And because they are GPS based they have the potential of being used where land based fixed radio navaids do not reach. All in all RNAV is more accurate and more flexible for procedure designers to use.But, again, in FS there is no difference. The math is the same when calculating position in the virtual world where it is all math anyway. However, I have no idea how accurate the FS coordinate system is but since it defines the world I think it is much, much better than any GPS so radio system accuracy is rather irrelevant. Mountains do not bounce radio wave around (not even sure if they block radio signals or not), storms don't monkey with reception and a 90 radial is 90 degrees as the math does not have a tolerance like real world radios do. One can consider FS radios spot on all the time.Did this answer your question?RegardsTerry

[contractpilot 12]

Terry,Thanks for your prompt and factual reply. I first noticed the FMS STARs when finalizing my approach into KMSP. I think my preference will be the RNAV approaches when required.Paul KuhnKGYR