The FMS/GPS unit’s nonsequencing mode provides an easy way to fly missed approach procedures, such as the one illustrated in Figure 3-56.
The missed approach procedure shown in Figure 3-56 requires you to climb to 1,900 feet, turn right and climb to 6,000 feet, then proceed direct to the SNS VOR.
The FMS/GPS helps you navigate between waypoints, which are geographically fixed locations. But where will the aircraft reach 1,900 feet on the missed approach procedure at Monterey? This depends on what aircraft you are flying and the chosen rate of climb. A single-engine airplane might be four miles away by the time it reaches 1,900 feet. A small jet might reach 1,900 feet by the end of the runway. The problem is that, given the way the FMS/GPS system uses waypoints, there is no one way to represent the climbs and turns required on a missed approach procedure.
To address this issue, all FMS/GPS RNAV units automatically suspend waypoint sequencing when you reach the missed approach point. The unit waits until you acknowledge the passing of the MAP before it continues the sequencing. When the aircraft has gained the published altitudes and complied with the initial MAP procedures, you can safely proceed to the missed approach holding waypoint, being mindful of any altitude requirements. A waypoint for the missed approach holding point is included as part of the missed approach procedure. In the example above, you can make the missed approach holding waypoint the active waypoint, and re-engage the sequencing mode upon reaching 6,000 feet. You now have sequencing mode guidance to the missed approach holding waypoint. The procedure for one FMS/GPS is illustrated in Figure 3-57.
Since the hold at SNS is part of the published missed approach procedure, it can be carried out using the same technique used to perform a holding pattern. Some FMS/GPS units will automatically switch to the nonsequencing mode when you reach the hold fix. Other units may advise you to switch manually to the nonsequencing mode.
Recognizing the Missed Approach Point
With any type of navigation equipment, it is important to be able to determine when you have reached the missed approach point. The missed approach point indications given by FMS/GPS units are sometimes subtle. Consider the two navigation displays shown in Figure 3-58. The display in the top graphic of Figure 3-58 shows the aircraft approaching the missed approach point, 1.4 NM away.
Now consider the display in the bottom graphic of Figure 3-58. The distance from the missed approach point might suggest that the aircraft is now even closer to the missed approach point. However, the TO/FROM flag on the course deviation indicator shows that the aircraft has in fact passed the missed approach point. It is tempting to monitor the distance from the missed approach point as it decreases to 0.0 NM. The problem is that, depending on how accurately the pilot flies, the distance may never reach 0.0 NM. Rather, it may simply begin to increase once you have passed abeam the missed approach point. It is, thus, important to check not only the distance from the missed approach point, but also the TO/FROM flag or arrow. In the rush of a missed approach, this small clue (arrow direction change) can be difficult to read and very easy to misinterpret.
Complying With ATC-Issued Missed Approach Instructions
ATC sometimes issues missed approach instructions that are different from those published on the approach chart. In this case, use the techniques described earlier to insert new waypoints into the route, and/or to intercept and track courses to those waypoints.
Setting Up Next Procedure in Hold
Once in the missed approach holding pattern, the next task is deciding where to go next and programming the new flight plan into the FMS/GPS unit. In this high workload situation, it is especially important to be very proficient with the menus, functions, and “switchology” of a particular unit. If the aircraft is equipped with an autopilot, it is also essential to have a thorough understanding of how the autopilot interacts and interfaces with the FMS/GPS navigation equipment.
Common Error: Noncompliance With Initial Missed Approach Instructions
The immense capability of the FMS/GPS may tempt you to follow its directions rather than fly a missed approach procedure exactly as published on the instrument approach procedure chart. Always fly procedures as published, especially with respect to the initial climb and turn instructions. GPS as a line-of-sight navigation aid can display courses and distances to a ground-based navaid even though the navaid is on the other side of a mountain range and itself cannot be received, because GPS signals are spaced based.
- Acknowledge a missed approach procedure.
- Set the FMS/GPS for a return to the same approach to fly it again.
- Select a different approach while holding at a missed approach holding waypoint.
- Program an ATC specified hold (user waypoint) point for selection after the published MAP/hold procedure.