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- FAA Changes Policy on the Use of GPS for Alternate Airports
- April 4, 2013
In a recent policy statement, the FAA announced a change to restrictions placed on GPS navigation systems with respect to alternate airport planning. Effective April 4, operators are now permitted to flight plan for a GPS approach at either the destination or an alternate, but not both. Previous policy only allowed the use of a GPS approach at the destination airport. Due to Sequestration cuts and the likelihood that VORs may be out-of-service (OTS) for long periods of time, allowing operators to plan for GPS approaches at alternate airports adds additional flexibility and will help alleviate delays. The new policy adds additional clarification for Wide Area Augmentation System (WAAS) users who plan to use WAAS vertical guidance at their alternate airport. Since GPS-based lateral guidance is the same for LNAV, LNAV/VNAV, and RNP 0.3 DA and approved barometric vertical navigation (baro-VNAV) equipment does not rely on GPS information, users of Wide Area Augmentation Systems (WAAS) with baro-VNAV equipment may plan for GPS approaches at both the destination and the alternate. The FAA conducted a review of the availability of GPS approaches throughout the National Airspace System (NAS) and determined that the policy change will not adversely affect operational safety in the NAS. Review the policy change.
- LightSquared Proposal Threatens GPS Integrity
- August 8, 2011
In January, the Federal Communications Commission (FCC) conditionally allowed a company called LightSquared to offer wireless broadband services in radio frequency bands adjacent to those used by GPS receivers. Based on feedback from public and private sector GPS users, the FCC told LightSquared that it could not launch service until testing could be completed to determine the extent of the problems that their proposal would cause. Learn More.
The Global Positioning System (GPS) is a space-based radio-navigation system consisting of a constellation of satellites and a network of ground stations used for monitoring and control. A minimum of 24 GPS satellites orbit the Earth at an altitude of approximately 11,000 miles providing users with accurate information on position, velocity, and time anywhere in the world and in all weather conditions.
Receiver Autonomous Integrity Monitor (RAIM)
Receiver Autonomous Integrity Monitor (RAIM) is a form of integrity monitoring performed within the avionics themselves. It ensures available satellite signals meet the integrity requirements for a given phase of flight. By comparing the distance measurements of a number of satellites, the RAIM function can identify a satellite failure and issue an alert to the pilot. Without RAIM capability, the pilot has no assurance of the accuracy of the GPS position. A minimum of five satellites is required to detect a bad satellite; at least six satellites are required to detect and exclude a bad satellite from the navigation solution if your receiver has a fault detection and exclusion (FDE) RAIM algorithm. The GPS receiver should also tell you when its RAIM function is unavailable, at both present time/position and at any selected future time/position. You can get information on satellite outages through the NOTAM system, however the effect of an outage on the intended operation cannot be determined unless the pilot has a RAIM availability prediction program which allows excluding a satellite which is predicted to be out of service.
If you are using GPS to fly an approach and you receive a RAIM annunciation prior to the final approach waypoint, you may not have sufficient accuracy to complete the approach.
You can get information on satellite outages through the NOTAM system, however the effect of an outage on the intended operation cannot be determined unless the pilot has a RAIM availability prediction program which allows excluding a satellite which is predicted to be out of service.
Satellite Based Augmentation System (SBAS)
The Satellite Based Augmentation System (SBAS) is an augment to the Global Positioning System (GPS) to enhance the accuracy and reliability of position estimates. The U.S. version of the Satellite Based Augmentation System (SBAS) has traditionally been referred to as the Wide Area Augmentation System. WAAS covers nearly all of the U.S. National Airspace System (NAS). Correction messages are broadcast by geostationary communication satellites. WAAS allows GPS to be used as a primary means of navigation from takeoff through Category I precision approach. The WAAS broadcast message improves GPS signal accuracy from 100 meters to approximately 7 meters.
Ground Based Augmentation System (GBAS)
The Ground Based Augmentation System (GBAS) is an augment the Global Positioning System (GPS) to improve aircraft safety during airport approaches and landings. The U.S. version of the Ground Based Augmentation System (GBAS) has traditionally been referred to as the Local Area Augmentation System (LAAS). The worldwide community has adopted GBAS as the official term for this type of navigation system. To coincide with international terminology, the FAA is also adopting the term GBAS to be consistent with the international community. GBAS is a ground-based augmentation to GPS that focuses its service on the airport area (approximately a 20-30 mile radius) for precision approach, departure procedures, and terminal area operations. It broadcasts its correction message via a very high frequency (VHF) radio data link from a ground-based transmitter. GBAS will yield the extremely high accuracy, availability, and integrity necessary for Category I, II, and III precision approaches, and will provide the ability for flexible, curved approach paths. GBAS demonstrated accuracy is less than one meter in both the horizontal and vertical axis.