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Local Area Augmentation System - How It Works

The Local Area Augmentation System (LAAS) will augment the Global Positioning System to improve aircraft safety during airport approaches and landings. LAAS will yield the extremely high accuracy, availability, and integrity necessary for Category I, II, and III precision approaches. It is expected that the end-state configuration will pinpoint the aircraft's position to within one meter or less with a significant improvement in service flexibility and user operating costs.

LAAS is comprised of ground equipment and avionics. The ground equipment includes 4 reference receivers, a LAAS ground facility, and a VHF data broadcast transmitter. This ground equipment is complemented by LAAS avionics installed on the aircraft.

Signals from GPS satellites are received by the LAAS GPS Reference Receivers (4 receivers for each LAAS) at the LAAS-equipped airport. The reference receivers calculate their position using GPS.

The GPS Reference Receivers and LAAS Ground Facility (or LGF) work together to measure errors in GPS-provided position. The LAAS Ground Facility produces a LAAS correction message based on the difference between actual and GPS-calculated position. Included in this message is suitable integrity parameters and approach path information.

This LAAS correction message is then sent to a VHF data broadcast (VDB) transmitter.

The VDB broadcasts the LAAS signal throughout the LAAS coverage area to avionics in LAAS-equipped aircraft.

LAAS provides its service to a local area (approximately a 20-30 mile radius). The signal coverage is designed support the aircraft's transition from en route airspace into and throughout the terminal area airspace.

The LAAS equipment in the aircraft uses the corrections provided on position, velocity, and time to guide the aircraft safely to the runway. This signal provides ILS-look-alike guidance as low as 200 feet above touchdown. LAAS will eventually support landings all the way to the runway surface.