System, Software and Complex Electronic Hardware Development

FAA Wide Area Augmentation System (WAAS) Safety Computer

The Wide Area Augmentation System was designed by the FAA to augment GPS technology to improve navigation accuracy, integrity and continuity for use by aircraft. The inherent errors in GPS did not permit use of GPS signals for the purposes of runway approach guidance. With WAAS, GPS guidance accuracy is improved to allow aircraft to conduct precision approaches to thousands of airports in the continental USA. Historically, many of these airports had no precision capabilities whatsoever. WAAS also supports the FAA’s NextGen initiative where technologies such as ADS-B improve air traffic flow and reduce workload on air traffic controllers.

WAAS consists of multiple ground reference stations positioned across the U.S. that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through 1 of 2 geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal. Navigation accuracy with WAAS is generally less than 3 meters.

Verocel was chosen by the FAA to design, certify and produce the safety computer for WAAS. The safety computer consists of a VME-based computer board with a Verocel-designed Field Programmable Gate Array (FPGA). The safety computer provides a hardware comparator that takes the outputs from two separate safety processors and ensures a bit-for-bit match in each message sent to the master station or uplink signal generators.

Verocel was also responsible for integration of the operating system and board support software used by the FAA’s WAAS application. Verocel performed DO-178C, Level B certification on the operating system and board support software. Verocel performed DO-254, DAL B certification on the hardware comparator.

Verocel has the production contract for the safety computer and chassis and ensures that each shipment meets the FAA’s stringent requirements for quality. Verocel’s safety computer can also be deployed in other ground-based GPS augmentation systems used in other countries.