The name of an instrument approach, as published, is  used to identify the approach, even if a component of the  approach aid is inoperative or unreliable. The controller  will use the name of the approach as published, but must  advise the aircraft at the time an approach clearance is  issued that the inoperative or unreliable approach aid  component is unusable. (Example: “Cleared ILS RWY 4,  glideslope unusable.”)  RNAV (GPS) approach procedures introduce their own  tracking issues because they are flown using an onboard  navigation database. They may be flown as coupled  approaches or flown manually. In either case, navigation  system coding is based on procedure design, including  waypoint (WP) sequencing for an approach and missed  approach. The procedure design indicates whether the WP  is a fly-over (FO) or fly-by (FB), and provides appropriate  guidance for each. A FB WP requires the use of turn  anticipation to avoid overshooting the next flight segment.  A FO WP precludes any turn until the WP is over flown and  is followed by either an intercept maneuver of the next  flight segment or direct flight to the next WP.  proceed via the holding fix that was the last assigned route,  and the feeder route associated with that fix, if a feeder  route is published on the approach chart, to the IAF to  commence the approach. When cleared for the approach,  the published off-airway (feeder) routes that lead from  the en route structure to the IAF are part of the approach  clearance.  If a feeder route to an IAF begins at a fix located along  the route of flight prior to reaching the holding fix,  and clearance for an approach is issued, a pilot should  commence the approach via the published feeder route.  For example, the aircraft would not be expected to overfly  the feeder route and return to it. The pilot is expected to  commence the approach in a similar manner at the IAF,  if the IAF for the procedure is located along the route of  flight to the holding fix.  If a route of flight directly to the IAF is desired, it should  be so stated by the controller with phraseology to include  the words “direct,” “proceed direct,” or a similar phrase  that the pilot can interpret without question. When a  pilot is uncertain of the clearance, ATC should be queried  immediately as to what route of flight is preferred.  Figure 4-9. Fly-by and fly-over waypoints.  4-18 Area Navigation Courses 