on its length, an arc requires you to follow a gradually  changing heading toward the active waypoint. The example  in  Figure 3-45  illustrates how an FMS is used to fly a DME  arc procedure. An IFR-capable GPS RNAV/FMS with qualified GPS  receiver(s) can be used as the sole means of navigation  for several kinds of instrument approach procedures, but  you need to know which approaches can be used with your  particular GPS RNAV unit. The following paragraphs review  the approaches available today. A GPS overlay approach is illustrated in  Figure 3-46.  The  basic benefit of the GPS overlay approach is that it allows  use of an IFR approved GPS receiver to navigate and fly a  conventional nonprecision approach. From the previous text,  you must know how to hold the specific sequences and how  the unit can be stopped from sequencing through the flight  plan. Many approaches require holding or a procedure turn  to orient the aircraft correctly for the approach course. If  you cannot control the sequencing of the FMS, you will lose  course guidance upon the turn for outbound holding, as the FMS/GPS receiver sequences for the course beyond the  holding fix. GPS overlay approaches are named for the conventional  system upon which the approach is based, but include the  word GPS. The approach in  Figure 3-46 is based on an  existing NDB approach. If the aircraft has an IFR‑approved  FMS/GPS RNAV, you may use that guidance to fly the GPS  overlay approach. It is not necessary for the aircraft to have  the conventional navigational equipment on board for that  approach, but conventional navigational avionics will be  required for any required alternate, if equipped with a TSO‑ 129 GPS receiver. If conventional avionics are installed in  the aircraft, there is no requirement to use the equipment in  any way, although monitoring is always a good practice. If  the installed FMS/GPS receiver is TSO-145A/146A WAAS  certified, no other navigation equipment is required. One common pitfall of all advanced avionics approaches is  the sometimes limited notification of the position along the  approach path. In many instances, you must read the name  of the waypoint to confirm where the aircraft is headed. It is  easy for you to be preoccupied with cross-check and flying  FMS and some GPS units simplify the problem of tracking  arcs, which are curved courses between waypoints. The  key feature of an arc is that there is no one bearing that  takes you from one waypoint to the next. Rather, depending  Mismanagement of the sequencing and nonsequencing  modes during a holding procedure is another common error.  Failing to switch the FMS/GPS RNAV to the nonsequencing  mode prior to reaching the holding waypoint, or prematurely  switching the unit back to the sequencing mode once  established in the hold, can prompt the FMS/GPS to sequence  past the holding waypoint. In this case, you are left without  guidance along the inbound holding course. Common Error: Mismanaging the Sequencing/ Nonsequencing Modes During a Hold GPS and RNAV (GPS) Approaches Essential Skills Essential Skills ARCS 1. Select a preprogrammed holding pattern, or  nonsequencing mode. 2. Select and setup a non‑preprogrammed holding pattern  inbound course. 3. Determine the proper sequence of software commands  for the holding pattern, transition to approach,  approach, and MAP navigation. 1. Select an approach procedure with an arc. 2. Select the course, or determine that automatic course  CDI setting will occur. Figure 3-44. A preprogrammed holding procedure. C RING MSG FPL PROC NRST OBS GPS COM  C V PWR VOL/ SQ PUSH VOL/ ID PUSH VLOC 116. 00 114. 10 COM 125.100 123. 850 NAV WRAPS DTK DIS BRG TRK GS ETE 0.6 124 130 nm m m  160 304 kt m 1. .0 00:05 _ _:_ _  C RING MSG FPL PROC NRST OBS GPS COM  C V PWR VOL/ SQ PUSH VOL/ ID PUSH VLOC 114. 10 116. 00 COM 125.400 123. 850 00 WAYPOINT DTK DIS ZOSON FA RW10 MA WRAPSMH hold ACTIVE FLIGHT PLAN KSJC / O27 M M  _ _ _ _ _ _ n  m  M  _ _ _ _ _ _ n  m  M  _ _ _ _ _ _ n  m  _ _:_ _ HOLD PARALLER A preprogrammed hold is indicated  by a special waypoint in the flight plan. The FMS automatically switches to the nonsequencing mode and sets the inbound course to the hold waypoint. The FMS displays the appropriate type of hold entry. C 125 100 1 0 The FMS automatically starts a timer for the outbound leg. 3-30