One of the geostationary satellites carrying the Wide Area Augmentation System (WAAS) signal won't be so stationary during the next 60 days. Satellite owner Inmarsat will be repositioning and re-aiming a satellite, shifting coverage to the west.
The move will have no effect on the vast majority of GPS users.
"But there may be times during the next two months when WAAS won't be available for precision vertical guidance," said Randy Kenagy, AOPA director of advanced technology. "That means you should check notams to make sure that LPV [lateral precision with vertical guidance] approach will be available when you want it."
The FAA leases space on two commercial satellites for its WAAS signal. The basic GPS signal, on the other hand, comes from 24 active satellites owned and operated by the U.S. military.
So that means the GPS signal that most pilots use with their handheld receivers or IFR en route and terminal operations-certified panel-mount units is controlled by Uncle Sam.
But the more precise WAAS signal, which provides vertical guidance (LNAV/VNAV and LPV instrument approaches) and advisory pseudo-glideslopes for GPS approaches, is somewhat at the mercy of commercial operators.
So after Inmarsat has its satellite parked in its new position with its antennas pointed farther west, WAAS coverage will be unavailable in the extreme northeast of the United States for most of the summer. That will affect LPV approaches in Portland, Maine, and Concord, New Hampshire.
Service there is scheduled to be restored this fall when the FAA buys space for WAAS on a third satellite owned by PanAmSat.
January 30, 2006