All IAPs must be retrievable from the current GPS database  supplied by the manufacturer or other FAA-approved  source. Flying point to point on the approach does not  assure compliance with the published approach procedure.  The proper RAIM sensitivity is not available and the CDI  sensitivity does not automatically change to 0.3 NM. Manually  setting CDI sensitivity does not automatically change  the RAIM sensitivity on some receivers. Some existing  nonprecision approach procedures cannot be coded for use  with GPS and are not available as overlays. GPS approaches are requested and approved by ATC using  the GPS title, such as “GPS RWY 24” or “RNAV RWY 35.”  Using the manufacturer’s recommended procedures, the  desired approach and the appropriate IAF are selected from  the GPS receiver database. Pilots should fly the full approach  from an initial approach waypoint (IAWP) or feeder fix unless  specifically cleared otherwise. Randomly joining an approach  at an intermediate fix does not ensure terrain clearance. When an approach has been loaded in the flight plan, GPS  receivers give an “arm” annunciation 30 NM straight  line distance from the airport/heliport reference point.  The approach mode should be “armed” when within 30  NM distance so the receiver changes from en route CDI  (±5 NM) and RAIM (±2 NM) sensitivity to ±1 NM terminal  sensitivity. Where the IAWP is within 30 NM, a CDI  sensitivity change occurs once the approach mode is armed  and the aircraft is within 30 NM. Where the IAWP is beyond  the 30 NM point, CDI sensitivity does not change until the  aircraft is within 30 NM even if the approach is armed earlier.  Feeder route obstacle clearance is predicated on the receiver  CDI and RAIM being in terminal CDI sensitivity within 30 NM  of the airport/heliport reference point; therefore, the receiver  should always be armed no later than the 30 NM annunciation. Pilots should pay particular attention to the exact operation of  their GPS receivers for performing holding patterns and in the  case of overlay approaches, operations such as procedure turns.  These procedures may require manual intervention by the pilot  to stop the sequencing of WPs by the receiver and to resume  automatic GPS navigation sequencing once the maneuver  is complete. The same WP may appear in the route of flight  more than once and consecutively (e.g., IAWP, final approach  waypoint (FAWP), missed approach waypoint (MAWP) on a  procedure turn). Care must be exercised to ensure the receiver  is sequenced to the appropriate WP for the segment of the  procedure being flown, especially if one or more fly-over WPs  are skipped (e.g., FAWP rather than IAWP if the procedure  turn is not flown). The pilot may need to sequence past one or  more fly-overs of the same WP in order to start GPS automatic  sequencing at the proper place in the sequence of WPs. A GPS missed approach requires pilot action to sequence the  receiver past the MAWP to the missed approach portion of  the procedure. The pilot must be thoroughly familiar with the  activation procedure for the particular GPS receiver installed  in the aircraft and must initiate appropriate action after the  MAWP. Activating the missed approach prior to the MAWP  Incorrect inputs into the GPS receiver are especially critical  during approaches. In some cases, an incorrect entry can  cause the receiver to leave the approach mode. Overriding an  automatically selected sensitivity during an approach cancels  the approach mode annunciation. If the approach mode is  not armed by 2 NM prior to the FAWP, the approach mode  does not become active at 2 NM prior to the FAWP and  the equipment will flag. In these conditions, the RAIM and  CDI sensitivity do not ramp down, and the pilot should not  descend to minimum descent altitude (MDA) but fly to the  MAWP and execute a missed approach. The approach active  annunciator and/or the receiver should be checked to ensure  the approach mode is active prior to the FAWP. When within 2 NM of the FAWP with the approach mode  armed, the approach mode switches to active, which results  in RAIM and CDI sensitivity changing to the approach  mode. Beginning 2 NM prior to the FAWP, the full scale  CDI sensitivity changes smoothly from ±1 NM to ±0.3 NM  at the FAWP. As sensitivity changes from ±1 NM to ±0.3  NM approaching the FAWP, and the CDI not centered,  the corresponding increase in CDI displacement may give  the impression the aircraft is moving further away from  the intended course even though it is on an acceptable  intercept heading. If digital track displacement information  (cross-track error) is available in the approach mode, it may  help the pilot remain position oriented in this situation.  Being established on the final approach course prior to the  beginning of the sensitivity change at 2 NM helps prevent  problems in interpreting the CDI display during ramp-down.  Requesting or accepting vectors, which causes the aircraft  to intercept the final approach course within 2 NM of the  FAWP, is not recommended. When receiving vectors to final, most receiver operating  manuals suggest placing the receiver in the nonsequencing  mode on the FAWP and manually setting the course. This  provides an extended final approach course in cases where  the aircraft is vectored onto the final approach course outside  of any existing segment that is aligned with the runway.  Assigned altitudes must be maintained until established on a  published segment of the approach. Required altitudes at WPs  outside the FAWP or step-down fixes must be considered.  Calculating the distance to the FAWP may be required in  order to descend at the proper location. 9-30