The US Federal Aviation Administration conducted the latest stage of its local area augmentation system (LAAS) flight testing this month. LAAS, based on use of the global positioning system (GPS), will replace the 40-year-old Cat 1/2/3 instrument landing systems operating in the USA.
The US agency had conducted LAAS feasibility tests with its Boeing 727 narrowbody, but the latest involved a UPS Boeing 767 making LAAS-based landing approaches at the FAA's technical centre near Atlantic City International Airport in New Jersey.
The UPS 767 made 39 approaches down to 25ft (8m) above the runway. The pilots flew some LAAS-assisted approaches manually, while others were coupled to the aircraft's autopilot. The flight tests studied the benefits of integrating a ground-based pseudolite into the FAA LAAS prototype.
In the pseudolite concept, a GPS-formatted signal is transmitted by the ground station to the aircraft, which replicates a GPS satellite. Integrity is an issue because of its sensitivity to satellite geometry and the time required to resolve the wavelength ambiguity. If contact is lost during an approach, the time taken to reacquire the signal and resolve the phase ambiguity could be outside that allowed for continued Cat 3 landing.
Source: Flight International
