Pilots who use some GPS units without WAAS (Wide Area Augmentation System) capabilities are encouraged to add a new task to their preflight list—RAIM checks.
The U.S. Terminal and En Route Area Navigation (RNAV) Operations, Advisory Circular AC90-100a, recommends that pilots check RAIM (receiver autonomous integrity monitoring) before flying area navigation (RNAV) standard instrument arrivals, departures, and obstacle departure procedures. It also suggests that RAIM be checked before flying RNAV routes known as Q and T routes (above and below 18,000 feet, respectively). The RAIM check is intended to prevent pilots who use advanced RNAV procedures and routes from flying into areas were GPS outages are expected to occur for more than five minutes.
As the FAA transitions to and implements the advisory circular, the agency has said that it will not start checking to see if pilots are following the guidelines in the AC until October. However, AOPA encourages pilots to go ahead and start making the checks now. AOPA, the FAA, and other industry and regulatory representatives worked together for a 90-day extension for compliance with the AC, which was previously set for July 1. During the next 90 days, AOPA will be working closely with FAA officials to ensure this new requirement can be accomplished seamlessly as part of the regular preflight planning process.
“Pilots/operators should not fly and/or perform their functions in fear of violations during this transition period,” the FAA told AOPA.
Pilots using WAAS-equipped GPS units in areas of WAAS coverage would not required to check RAIM but should continue to check GPS notams.
Pilots with non-WAAS-equipped GPS units can get current RAIM information from a flight service station briefer or online. RAIM prediction tools are also built into some GPS units such as the Garmin 430/530 series.