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WAAS Performances

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WAASWAAS
Title WAAS Performances
Author(s) GMV.
Level Basic
Year of Publication 2011
Logo GMV.png


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

Performances are usually described in terms of accuracy, integrity, availability and continuity. The WAAS specification Performance Requirements[7] are different depending on the phase of the flight: en route through 1) Non-precision approach (NPA) and 2) Precision Approach.

The WAAS Performance Requirements as specified in FAA Specification for the Wide Area Augmentation System(WAAS) document are the following;

1) WAAS Performance Requirements for Non-Precision Approach

Performances Requirements for Non-Precision Approach
Performance Requirement Total System Navigation System WAAS Signal-in-Space Airborne
Availability 0.999 0.999 0.999 Not Specified (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

10e-7/hour
8 s

N/S
2 s
Continuity
Continuity of Navigation
Continuity of Fault Detection

1 - 10e-5/hour
1 - (2x10e-5)/hour

1 - 10e-5/hour
1 - (2x10e-5)/hour

1 - 10e-8hour
1 - 10e-5/hour

1 - 10e-5/hour
1 - 10e-5/hour

2) WAAS Performance Requirements for Precision Approach

Performances Requirements for Precision Approach
Performance Requirement Total System Navigation System WAAS Signal-in-Space Airborne
Availability Not Specified (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

10e-7/approach
5.2 s

N/S
N/S
Continuity of Function
Continuity of Navigation
Continuity of Fault Detection
1 - 10e-4/approach
N/S
N/S
1 - 10e-4/approach
N/S
N/S
1 - (5.5x10e-5)/approach
N/S
N/S
1 - (4.5x10e-5)/approach
N/S
N/S

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]

Typical WAAS LPV Coverage

Notes

References