I was looking at the RNAV runway 35R APP into KDEN today and I saw at the top of the chart it says RNP-0.3.I know that that means 0.3NM. BUT, in 737 I was flying the FMC said that my ANP is 0.04NM. So to the question. Does an aircraft's ANP vary? OR is it a constant value that never changes?Is an aircraft's ANP based upon something to do with IRS?

ANP (Actual Navigation Performance) is the FMC reporting to you an estimate of how well it thinks it is doing as far as knowing exactly where it is, based on the data currently available to it.When every source it can use to determine its position from is available to the aircraft (i.e. it is in range of navaids, is getting GPS signals and the FMC is working in conjunction with the IRS), then ANP will be based on a combination of the navigation logic of the FMC, plus twin GPS signals, plus signals from two ground-based navaids, and is therefore very accurate, i.e. as good as being able to determine where it is with a less than 100 meter margin of error.But when over water there are not always suitable navaids in range, and the IRS can drift and both of them can differ slightly too, often quite a bit depending on the latitude, so the accuracy of the FMC's idea of where it is can diminish. Even when navaids are in range, their slant range can affect accuracy, particularly if the exact air pressure is unknown or on STD altimeter settings, since the exact height above the terrain would then be unknown too of course. This is why RNP values actually change depending on where the aircraft is, and why RNP prerequisites are different for various stages of a flight: Over oceans RNP is 4nm, en-route RNP is 2nm, in the terminal area RNP is 1nm and RNP is 0.3nm when on an approach.Al

ANP (Actual Navigation Performance) is the FMC reporting to you an estimate of how well it thinks it is doing as far as knowing exactly where it is, based on the data currently available to it.When every source it can use to determine its position from is available to the aircraft (i.e. it is in range of navaids, is getting GPS signals and the FMC is working in conjunction with the IRS), then ANP will be based on a combination of the navigation logic of the FMC, plus twin GPS signals, plus signals from two ground-based navaids, and is therefore very accurate, i.e. as good as being able to determine where it is with a less than 100 meter margin of error.But when over water there are not always suitable navaids in range, and the IRS can drift and both of them can differ slightly too, often quite a bit depending on the latitude, so the accuracy of the FMC's idea of where it is can diminish. Even when navaids are in range, their slant range can affect accuracy, particularly if the exact air pressure is unknown or on STD altimeter settings, since the exact height above the terrain would then be unknown too of course. This is why RNP values actually change depending on where the aircraft is, and why RNP prerequisites are different for various stages of a flight: Over oceans RNP is 4nm, en-route RNP is 2nm, in the terminal area RNP is 1nm and RNP is 0.3nm when on an approach.Al

Thanks so much for the info, really appreciate it.

ANP (Actual Navigation Performance) is the FMC reporting to you an estimate of how well it thinks it is doing as far as knowing exactly where it is, based on the data currently available to it.When every source it can use to determine its position from is available to the aircraft (i.e. it is in range of navaids, is getting GPS signals and the FMC is working in conjunction with the IRS), then ANP will be based on a combination of the navigation logic of the FMC, plus twin GPS signals, plus signals from two ground-based navaids, and is therefore very accurate, i.e. as good as being able to determine where it is with a less than 100 meter margin of error.But when over water there are not always suitable navaids in range, and the IRS can drift and both of them can differ slightly too, often quite a bit depending on the latitude, so the accuracy of the FMC's idea of where it is can diminish. Even when navaids are in range, their slant range can affect accuracy, particularly if the exact air pressure is unknown or on STD altimeter settings, since the exact height above the terrain would then be unknown too of course. This is why RNP values actually change depending on where the aircraft is, and why RNP prerequisites are different for various stages of a flight: Over oceans RNP is 4nm, en-route RNP is 2nm, in the terminal area RNP is 1nm and RNP is 0.3nm when on an approach.Al

Just to add to that, the rnp is 10 nm required over non radar oceanic and as well you can get down to .1 on approaches.JackColwill

Just to add to that, the rnp is 10 nm required over non radar oceanic and as well you can get down to .1 on approaches.JackColwill

It is also worth noting regarding RNP that during the approach phase (particularly when using RNP-AR approaches) many airlines disable VOR and DME updating as those inputs can pollute the navigation solution.GPS derived information alone is used to ensure a nav solution of high integrity.

It is also worth noting regarding RNP that during the approach phase (particularly when using RNP-AR approaches) many airlines disable VOR and DME updating as those inputs can pollute the navigation solution.GPS derived information alone is used to ensure a nav solution of high integrity.

Yeah we used to disable it but we dont any more.JackColwill