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WAAS Performances
| WAAS | |
|---|---|
| Title | WAAS Performances |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
The Wide Area Augmentation System (WAAS) is the United States Satellite Based Augmentation System. The programme, started in 1992, is being carried out by the Federal Aviation Agency (FAA)[1] and is specially developed for the civil aviation community.[2] The system, which was declared operational in late 2003,[3] currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada.[4] WAAS service area includes CONUS, Alaska, Canada and Mexico.[5] The WAAS programme is continuously in evolution; two development phases have been already covered, a third is in progress, and there are plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.[6]
WAAS Performances
Satellite Based Augmentation Systems (SBAS) performances are usually described in terms of integrity, accuracy, availability, and continuity. The WAAS specification performance requirements[7] depend on the phase of the flight: 1) en route through non-precision approach (NPA) and 2) precision approach.
According to its specification document, WAAS performance requirements are the following:[7]
- 1. WAAS Performance Requirements for En Route through 'Non-Precision Approach'
| Performance Requirement | Total System | Navigation System | WAAS Signal-in-Space | Airborne |
|---|---|---|---|---|
| Availability | 0.99999 | 0.99999 | 0.99999 | N/S |
| Accuracy 95% Horizontal Position 99.999% Horizontal Position 95% Vertical Position 95% Pseudorange |
N/S N/S N/A N/A |
100 m 500 m N/A N/S |
N/S N/S N/A N/S |
N/S N/S N/A 1.2 m |
| Integrity Integrity Risk Time-to-Alarm |
N/S 10 s |
N/S 10 s |
10-7/hour 8 s |
N/S 2 s |
| Continuity Continuity of Navigation Continuity of Fault Detection (1) |
1 - 10-5/hour 1 - (2x10-5)/hour |
1 - 10-5/hour 1 - (2x10-5)/hour |
1 - 10-8/hour 1 - 10-5/hour |
1 - 10-5/hour 1 - 10-5/hour |
- (1) Excluding outages of less than 5 minutes.
- 2. WAAS Performance Requirements for Precision Approach
| Performance Requirement | Total System | Navigation System | GPS/WAAS Signal-in-Space | Airborne |
|---|---|---|---|---|
| Availability | N/S | N/S | 0.999 | N/S |
| Accuracy 95% Horizontal Position 95% Vertical Position 95% Pseudorange |
33.5 m 9.8 m N/A |
7.6 m 7.6 m N/S |
N/S N/S N/S |
N/S N/S 1.2 m |
| Integrity Integrity Risk Time-to-Alarm |
N/S N/S |
N/S N/S |
10-7/approach 5.2 s |
N/S N/S |
| Continuity Continuity of Navigation Continuity of Fault Detection |
1 - 10-4/approach N/S N/S |
1 - 10-4/approach N/S N/S |
1 - (5.5x10-5)/approach N/S N/S |
1 - (4.5x10-5)/approach N/S N/S |
- N/S stands for Not Specified.
- N/A stands for Not Applicable.
On July 10, 2003, the WAAS system was certified for for safety-of-life aviation, covering 95% of the United States, and portions of Alaska [3][8]. At present, WAAS supports en-route, terminal and approach operations down to a full LPV-200 (CAT-I like Approach Capability) for the CONUS, Mexico and Canada. Typical performances provided by WAAS System when considering operating in LPV (Horizontal Alarm Limit = 40 m , Vertical Alarm Limit =50 m) are shown in next figure:[9]
WAAS Signal-In-Space Performance Requirements
According to the WAAS peformance standard[10] WAAS service area is divided in five coverage zones:
- Zone 1: CONUS.
- Zone 2: Alaska.
- Zone 3: Hawaii.
- Zone 4: Puerto Rico and some other Caribean islands.
- Zone 5: US territory excluding zones 1 to 4.
The volume covered includes a region up to 100.000 feet above the surface. For zones 1 to 4, the area extends up to 30 nm outside the land.
The requirements considering the different flight phases and the different coverage zones are summarised in the next table:[10]
| En Route | Terminal | LNAV | LNAV/VNAV | LPV | LPV 200 | |
|---|---|---|---|---|---|---|
| TTA | 15 s | 15 s | 10 s | 10 s | 6.2 s | 6.2 s |
| HAL | 2 nm | 1 nm | 556 m | 556 m | 40 m | 40 m |
| VAL | N/A | N/A | N/A | 50 m | 50 m | 35 m |
Notes
References
- ^ Navigation Services - History - Satellite Navigation, FAA.
- ^ Navigation Services - Wide Area Augmentation System (WAAS), FAA.
- ^ a b Wide Area Differential GPS (WADGPS), Stanford University
- ^ GNSS - GPS/WAAS Approaches, Federal Aviation Agency (FAA).
- ^ WAAS Service Expanded into Canada and Mexico, September 28, 2007, Federal Aviation Agency (FAA).
- ^ SatNav News, Vol. 33, March 2008, Federal Aviation Agency (FAA).
- ^ a b Specification for the Wide Area Augmentation System (WAAS), FAA-E- 2892b, August 13, 2001, FAA.
- ^ Wide Area Augmentation System
- ^ FAA Monitoring WAAS Performances in Real-Time
- ^ a b Global Positioning System Wide Area Augmentation System (WAAS) Performance Standard, Department of Transportation and Federal Aviation Administration, USA, 1st Edition, 31 October 2008.