WAAS Performances

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

The Wide Area Augmentation System (WAAS) is an GPS Augmentation system developed by the Federal Aviation Administration (FAA), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.

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.

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

2) 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

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