Handheld GPS Units

VFR and handheld GPS systems are not authorized for IFR navigation, instrument approaches, or as the principal instrument flight reference. During IFR operations, they may be considered only as an aid to situational awareness. This restriction is due to the following reasons: 

1. RAIM Capability – VFR GPS receivers and all handheld units have no RAIM alerting capability. Loss of the required number of satellites in view, or the detection of a position error, cannot be displayed to the pilot by such receivers. 

2. Database Currency – In certified GPS receivers, an updatable database is used for navigation fixes, airports, and instrument procedures. These databases must be maintained to the current update for IFR operation, but no such requirement exists for handheld units.

3. Antenna Location – In many VFR installations of GPS receivers, antenna location is more a matter of convenience than performance. In IFR installations care is exercised to ensure that an adequate clear view is provided for the antenna to see satellites. If an alternate location is used, some portion of the aircraft may block the view of the antenna, causing a greater opportunity to lose reception.

4. Battery Operation—Handheld GPS units are less reliable because they are not hardwired into the aircraft’s primary electrical system. They are dependent upon batteries or an AC adaptor as a power source.

Alternate Navigation Equipment

Aircraft using GPS navigation equipment under IFR must be equipped with an approved and operational alternate means of navigation appropriate to the flight (typically a VOR receiver). When weather at the primary destination does not meet the 1-2-3 Rule and an alternate airport is required in the flight plan, the alternate airport must have a non-GPS approach for which you are equipped. Active monitoring of alternative navigation equipment is not required if the GPS receiver uses RAIM for integrity monitoring. Active monitoring of an alternate means of navigation is required when the RAIM capability of the GPS equipment is lost. Aircraft equipped with a WAAS GPS receiver may use WAAS GPS as a primary means of navigation. No additional equipment is required.

RAIM

The GPS receiver verifies the integrity (usability) of the signals received from the GPS constellation through receiver autonomous integrity monitoring (RAIM) to determine if a satellite is providing corrupted information. At least one satellite, in addition to those required for navigation, must be in view for the receiver to perform the RAIM function; thus, RAIM needs a minimum of five satellites in view, or four satellites and a barometric altimeter (baro-aiding) to detect an integrity anomaly.

During pre-flight FSS briefings, Pilots should specifically request GPS NOTAMS as well as en route and terminal RAIM checks. Briefers will provide RAIM information for a period of one hour before to one hour after the ETA, unless a specific time frame is requested by the pilot.

On long trips, the AIM suggests periodic destination RAIM checks. Systems such as the Garmin G1000 provide a RAIM Prediction Tool  which can be accessed by checking the AUX-GPS Status page. A RAIM AVAILABLE message should be displayed which is valid +/- 15 minutes of the specified arrival date and time. WAAS approaches do not require a RAIM check—WAAS-equipped GPS units do this automatically.

If RAIM is unavailable, you will not be offered GPS approaches when you attempt to load a procedure. If you loaded a procedure beforehand when RAIM was available, it will not activate.

If RAIM capability is lost while conducting IFR en route or during approach, you cannot continue flight using GPS information alone. Without RAIM capability, the GPS may no longer be providing the required accuracy. The pilot should select another type of navigation system until RAIM is restored. On systems such as the Garmin G1000, inconsistent position solutions will trigger a RAIM warning. An LOI (Loss of Integrity) advisory will appear in the center of the HSI. On the approach, RAIM UNAVAIL or ABORT APR means that GPS navigation has been lost between the Final and Missed Approach waypoints and a missed approach should be implemented.

Types of GPS approaches:

1. GPS overlay of pre-existing non-precision approaches. 

2. VOR/DME-based RNAV approaches. 

3. Stand-alone RNAV (GPS) approaches. 

4. RNAV (GPS) approaches with vertical guidance (APV). 

5. RNAV (GPS) precision approaches (WAAS and LAAS).

The terms RNAV and VNAV are found in the minimums section of RNAV (GPS) approach plates and indicate an instrument approach with lateral and/or vertical guidance. LNAV-only approaches will depict minimum altitude as MDA and LNAV/VNAV minimums will be depicted as decision altitude (DA).

The GPS Approach Overlay Program is an authorization for pilots to use GPS avionics under IFR for flying designated non-precision instrument approach procedures, except LOC, LDA, and SDF procedures. These procedures are now identified by the name of the procedure and "or GPS" (e.g., VOR/DME or GPS RWY 15). Only approaches contained in the current onboard navigation database are authorized. 

A GPS stand alone approach consists of a sequence of waypoints defining the point-to-point track to be flown coded into the database, including the initial approach, intermediate, final approach, missed approach, missed approach turning, and missed approach holding waypoints. All waypoints, except a missed approach waypoint at the runway threshold, will be named with a five-letter alpha character name. Missed approach waypoints at the threshold will be assigned a database identifier. The sequence of waypoints appearing in the display should be identical to the waypoint sequence appearing on an associated approach chart.

Terminal Arrival Area (TAA) is controlled airspace established in conjunction with the standard or modified RNAV approach configurations. It provides a seamless transition from the enroute structure to the terminal environment for arriving aircraft equipped with FMS and/or GPS navigational equipment. The TAA provides a NoPT for aircraft using the approach and has three standard areas: straight-in, left base, and right base. The arc boundaries of the three areas are published portions of the approach and allow aircraft to transition from the enroute structure direct to the nearest IAF.

Many of the original overlay approaches have been replaced with stand-alone procedures specifically designed for use by GPS systems. The title of the remaining GPS overlay procedures has been revised on the approach chart to "or GPS" (e.g., VOR or GPS RWY 24). Therefore, all the approaches that can be used by GPS now contain "GPS" in the title (e.g., "VOR or GPS RWY 24," "GPS RWY 24," or "RNAV (GPS) RNY 24"). During these GPS approaches, underlying ground-based NAVAIDS are not required to be operational and associated aircraft avionics need not be installed, operational, turned on or monitored (Monitoring of the underlying approaches is suggested when equipment is available and functional). Existing overlay approaches may be requested using the GPS title, such as "GPS RWY 24" for the VOR or GPS RWY 24.

Suitable RNAV systems (TSO-C129/-C145/-C146) may be used in the following ways: 

1. Determine aircraft position over or distance from a VOR, TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course. 

2. Navigate to or from a VOR, TACAN, NDB, or compass locator. 

3. Hold over a VOR, TACAN, NDB, compass locator, or DME fix.

4. Fly an arc based upon DME. 

Note: These operations are allowable even when a facility is explicitly identified as required on a procedure (e.g., "Note ADF required"). Also, these operations do not include navigation on localizer-based courses (including localizer back course guidance). Restrictions that apply to the use of GPS as a substitute for ADF and/or DME: Waypoints, fixes, intersections, and facility locations to be used for these operations must be retrieved from the GPS airborne database. The database must be current. If the required positions cannot be retrieved from the airborne database, the substitution of GPS for ADF and/or DME is not authorized. When using a facility as the active waypoint, the only acceptable facility is the DME facility which is charted as the one used to establish the DME fix. If this facility is not in your airborne database, you are not authorized to use a facility waypoint for this operation.

Any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate.

Wide area augmentation system (WAAS) is a satellite navigation system consisting of the equipment and software which augments the GPS Standard Positioning Service (SPS). The WAAS provides enhanced integrity, accuracy, availability, and continuity over and above GPS SPS. The differential correction function provides improved accuracy required for precision approaches. Aircraft equipped with an approved WAAS receiver can use GPS as the primary navigation system from takeoff through a Category 1 precision approach.

Approach with Vertical Guidance (APV) is a new class of approach procedures that provides vertical guidance, but does not meet the ICAO Annex 10 requirements for precision approaches. These new procedures are defined in ICAO Annex 6, and include approaches such as the LNAV/VNAV procedures presently being flown with barometric vertical navigation (Baro-NAV). These approaches provide vertical guidance, but do not meet the more stringent standards of a precision approach. Properly certified WAAS receivers will be able to fly these LNAV/VNAV procedures using a WAAS electronic glide path, which eliminates the errors that can be introduced by using barometric altimetry.

Localizer Performance with Vertical Guidance (LPV) is a new type of APV approach procedure, in addition to LNAV/VNAV, which takes advantage of the high accuracy guidance and increased integrity provided by WAAS. This angular guidance allows the use of TERPs approach criteria used for ILS approaches. The resulting approach procedure minima (LPV) may have decision altitudes as low as 200 feet height above touchdown with visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest minima. LPV minima are published on the RNAV (GPS) approach charts. Receivers capable of flying LPV procedures must contain a statement in the Flight Manual Supplement or Approved Supplemental Flight Manual stating that the receiver has LPV capability, as well as the capability for the other WAAS and GPS approach procedure types.