Italia,
Again, I dont know about non-commercial units, nor the Garmin.
Most of the data that I have provided is either from the Honeywell or Smiths manuals.
As for coverage in Canada, I dont know if Canada has full implementation of WAAS yet, or even how many WAAS procedures there are out there.
As for the augmentation, this is very important to remember, it is simply a correction factor for the particular sat, defining it for the ac receiver to use. It is not a rebroadcast of a GPS signal, or a stand alone navigation signal, it is simply a correction factor.
The sat is happy to orbit broadcasting its signal. The WAAS computers are looking at each sat, the signal, position, geodetic position, atmospheric conditions, etc, and broadcasting this correction factor through the WAAS sat, for your receiver to use.
Perhaps this will help on RAIM.
Receiver Autonomous Integrity Monitoring - Wikipedia, the free encyclopedia
Note that online RAIM
prediction tools are dispatch level tools, just to give you an idea of the potential coverage. As I stated before, there are many GPS only arrival/departure procedures, that if the RAIM prediction is below a certain level, the ac cannot depart.
RAIM is an internal function of the GPS receiver on the ac or ABAS, meaning it is an aircraft based augmentation system, WAAS is sat based augmentation, and GBAS is ground based. These are an augmentation that further define the internal algorithms for higher accuracy values. This is why you must have a specific WAAS or GBAS capability. The ac is still required to correct and balance the GPS for nav, even without external augmentation.
How each system uses data, couples with other data such as the IRU, is specific to the manufacturer.
One has to remember that these are real time measurements, with the unit having different latency values, depending on the unit and equipage. In flight the unit is polling all of the other units and returning the estimated position. While this happens very quickly, the ac is also moving very quickly. While a latency value of 0.74 seconds to poll appears a very short time, the ac has gone how far in that amount of time? When you look at accuracy down to 10 m, this is quite an accomplishment.
When one views the estimated position vs required, the estimated position is the EPE as currently defined in the criteria. While the terminology may be evolving or be proprietary, it is understood what the foundation of the calculations is based on.
It appears that your Garmin is saying the same as I stated for EPE. In your example, that "
The accuracy of the aircraft’s GPS fix is calculated using Estimated Position Uncertainty (EPU), Dilution of Precision (DOP), and horizontal and vertical figures of merit (HFOM and VFOM). EPU is a statistical error indication and not an actual error measurement.
Note Accuracy, ie EPE is calc'd USING....it also states EPU is NOT the actual error measurement.
We are talking about the same value for HFOM and VFOM, these are values that talk into account the IRU.
The example that I provided for TSE was for vertical navigation position, your example is for horizontal navigation.
HAL is certainly a function of the unit, options, and coupled equipment. In my example, the units will go to a hybrid HIL, depending on configuration, and provide an 'equivalent' HIL. Depending on the IRU updating capability, the timeframe on on the equivalent will vary.
While the HAL is based on 2 times the selected level, how the units derive this estimate varies. In my example, the Smiths box on the 737-700 went to HAL at 0.51, with .3RNP selected, not 0.60.
Here is something else that we must consider in GPS navigation, the latency to config between levels and/or phases. The ac must calc and configure all of the variables prior to use. This becomes an issues sometimes, especially when going from RNP 1.0 to RNP .3 and especially RNP .1. If the procedure at waypoint A is RNP .1, then the ac must be configured prior to crossing waypoint A. All systems must be on board, and this takes some time.
When the unit is doing a check 2nm from FAF, that is a final check, and everything is configured for the final segment, prior to the FAF, not beginning at the FAF. Depending on the change in RNP or required levels, the unit must config further back than 2nm...