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) and is specially developed for the civil aviation community. The system, which was declared operational in late 2003, currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada. WAAS service area includes CONUS, Alaska, Canada and Mexico. 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.

WAAS Performances

Performances are usually described in terms of accuracy, integrity, availability and continuity. The WAAS specification Performance Requirements 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 are summarized in the following table

Performances Requirements for Non-Precison 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

1. WAAS Performance Requirements for Precision Approach are summarized in the following table:

Performances Requirements for Precison 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 signal was activated for safety-of-life aviation, covering 95% of the United States, and portions of Alaska . 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:

Typical WAAS LPV Coverage