Definition
A ground-based augmentation to GPS that improves the accuracy, integrity, and availability of GPS signals within the local area surrounding an airport, enabling precision instrument approaches down to and including Category I, II, and III minimums. A LAAS installation consists of GPS reference receivers at known surveyed positions on the airport, a central processing facility, and a VHF data broadcast transmitter that sends correction and integrity data to suitably equipped aircraft. LAAS has since been formally renamed the Ground Based Augmentation System (GBAS) by the FAA and ICAO.
Plain English
A system of equipment installed at an airport that fixes small errors in GPS signals and broadcasts the corrections to aircraft nearby, so they can fly very accurate GPS-based approaches to that airport.
Context Anchor
Seen on instrument approach chart and navigation-equipment discussions for GPS-based approaches that use local airport corrections.
Derivation
"Local Area" indicates the corrections are valid only within roughly 20–30 nautical miles of the airport where the equipment is installed, in contrast to the Wide Area Augmentation System (WAAS), which covers continental areas. "Augmentation" means adding to or strengthening — here, strengthening the basic GPS signal with extra correction data.
Why Pilots Care
It supplies the accuracy and integrity needed for Category I precision approaches at equipped airports where WAAS coverage may be limited.
Intuition Check
Do not read “augmentation” as a separate navigation system replacing GPS. LAAS adds local corrections and safety checks to GPS for equipped aircraft near the airport.
Example Sentence 1
The airport's LAAS installation allows properly equipped aircraft to fly precision GPS approaches in low-visibility conditions.
Example Sentence 2
LAAS corrections allowed the aircraft to maintain the required lateral and vertical guidance down to decision altitude.