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Navigation Aids


There are generally two types of RAIM fault messages. The first type of message indicates that there

are not enough satellites available to provide RAIM integrity monitoring. The GPS navigation solution may be
acceptable, but the integrity of the solution cannot be determined. The second type indicates that the RAIM
integrity monitor has detected a potential error and that there is an inconsistency in the navigation solution for
the given phase of flight. Without RAIM capability, the pilot has no assurance of the accuracy of the GPS


Selective Availability.  Selective Availability (SA) is a method by which the accuracy of GPS is

intentionally degraded. This feature was designed to deny hostile use of precise GPS positioning data. SA was
discontinued on May 1, 2000, but many GPS receivers are designed to assume that SA is still active. New
receivers may take advantage of the discontinuance of SA based on the performance values in ICAO Annex 10.

b. Operational Use of GPS. 

U.S. civil operators may use approved GPS equipment in oceanic airspace,

certain remote areas, the National Airspace System and other States as authorized (please consult the applicable
Aeronautical Information Publication). Equipage other than GPS may be required for the desired operation. GPS
navigation is used for both Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) operations.

1. VFR Operations


GPS navigation has become an asset to VFR pilots by providing increased navigational capabilities

and enhanced situational awareness. Although GPS has provided many benefits to the VFR pilot, care must be
exercised to ensure that system capabilities are not exceeded. VFR pilots should integrate GPS navigation with
electronic navigation (when possible), as well as pilotage and dead reckoning.


GPS receivers used for VFR navigation vary from fully integrated IFR/VFR installation used to

support VFR operations to hand

held devices. Pilots must understand the limitations of the receivers prior to

using in flight to avoid misusing navigation information. (See TBL 1


6.) Most receivers are not intuitive. The

pilot must learn the various keystrokes, knob functions, and displays that are used in the operation of the receiver.
Some manufacturers provide computer

based tutorials or simulations of their receivers that pilots can use to

become familiar with operating the equipment.


When using GPS for VFR operations, RAIM capability, database currency, and antenna location are

critical areas of concern.


RAIM Capability. VFR GPS panel mount receivers and hand

held units have no RAIM alerting

capability. This prevents the pilot from being alerted to the loss of the required number of satellites in view, or
the detection of a position error. Pilots should use a systematic cross

check with other navigation techniques to

verify position. Be suspicious of the GPS position if a disagreement exists between the two positions.


Database Currency. Check the currency of the database.  Databases must be updated for IFR

operations and should be updated for all other operations. However, there is no requirement for databases to be
updated for VFR navigation. It is not recommended to use a moving map with an outdated database in and around
critical airspace. Pilots using an outdated database should verify waypoints using current aeronautical products;
for example, Chart Supplement U.S., Sectional Chart, or En Route Chart.


Antenna Location. The antenna location for GPS receivers used for IFR and VFR operations may

differ. VFR antennae are typically placed for convenience more than performance, while IFR installations
ensure a clear view is provided with the satellites. Antennae not providing a clear view have a greater opportunity
to lose the satellite navigational signal. This is especially true in the case of hand

held GPS receivers. Typically,

suction cups are used to place the GPS antennas on the inside of cockpit windows. While this method has great
utility, the antenna location is limited to the cockpit or cabin which rarely provides a clear view of all available
satellites.  Consequently, signal losses may occur due to aircraft structure blocking satellite signals, causing a
loss of navigation capability. These losses, coupled with a lack of RAIM capability, could present erroneous
position and navigation information with no warning to the pilot. While the use of a hand

held GPS for VFR

operations is not limited by regulation, modification of the aircraft, such as installing a panel

 or yoke


holder, is governed by 14 CFR Part 43. Consult with your mechanic to ensure compliance with the regulation
and safe installation.