Is Autopilot NAV setting useful?

Question

In flight simulator, using the NAV setting directs the Autopilot to follow the FMS' pre-setup flight plan and will navigate the aircraft through each of the configured waypoints.

In real life, however, it seems almost a guarantee that ATC will provide some heading which is not necessarily the most direct route, ie. what your flight plan had configured. ATC will request you turn right or left somewhere around the waypoint you expected, but not where you or the NAV system would have turned.

Even in the simulator, if you use the built-in ATC, it will give headings that are not what the flight plan had expected... making the NAV button not very useful except when flying VFR without following.

It seems the autopilot HDG feature is used more often. Is this true in real life as well?

Answer 1

In flight simulator, using the NAV setting directs the Autopilot to follow the FMS' pre-setup flight plan and will navigate the aircraft through each of the configured waypoints.

No. The NAV mode follows VOR radial. The FMS might provide "virtual vor" and use NAV mode too, but usually there is a separate LNAV mode for FMS.

In real life, however, it seems almost a guarantee that ATC will provide some heading which is not necessarily the most direct route, ie. what your flight plan had configured. ATC will request you turn right or left somewhere around the waypoint you expected, but not where you or the NAV system would have turned.

No.

1. In real life, most of the time you follow the flight plan. And even if the ATC wants you to fly other route, they will tell you new set of routes or fixes to use and you punch them in the FMS, so you still fly LNAV.

2. Exception is approach where it is common that ATC will have you fly downwind (opposite direction than the runway) and tell you to turn base and intercept the final approach, so there they will give you heading (and you use HDG mode on the A/P). But that is once during the flight. Sometimes also once on departure, but that's usually it.

3. The ATC can also tell you to follow some radial of some VOR and that's where you use the NAV mode proper, not the LNAV mode used for following FMS.

4. Your flight plan is usually not direct, but follows the defined airways.

Even in the simulator, if you use the built-in ATC, it will give headings that are not what the flight plan had expected... making the NAV button not very useful except when flying VFR without following.

I am not sure how realistic the simulator ATC is and would't expect much of it. You'd get a better result in something like IVAO where the controllers are played by real people.

It seems the autopilot HDG feature is used more often. Is this true in real life as well?

The HDG feature is used when the ATC vectors you around. It usually happens on busy airports on approach and on really busy airports on departure, but enroute it is rare.

The LNAV feature is used most of the time. The NAV feature is indeed rare, because most of the time you use FMS, not a raw VOR.

Answer 2

There are essentially two scenarios on departure: an initial vector, or flying the departure procedure track immediately "off the ground."

In the former case, the instructions might be along the lines of, "fly heading 120, expect vectors to JEBBB" or "... to join the WHOZT5 departure." In that case, shortly after takeoff, the pilot would select Heading mode and fly the specified heading. At some point after that, ATC would issue a clearance to proceed direct to a fix, and then the filed route would be flown from that point on. So upon receiving this clearance, the pilot would proceed direct to the given waypoint by engaging NAV (or, given modern nomenclature, LNAV).

In the other case, the first leg of the departure corresponds to the "straight ahead" track of the departure runway, and LNAV is activated immediately after departure, and the aircraft will fly the magenta line as published. So in this case, Heading mode isn't used, unless ATC needs to vector the aircraft off of the published track. In that case, they can either issue a vector, or they can clear the aircraft to a later point in the procedure or along the route.

In modern ATC, it is very uncommon for an aircraft to be getting vectors enroute, simply because it is more workload for the controller with no benefit. Once you're away from the terminal area, they clear you on whatever route you've filed (or been assigned), and they don't have to do any more navigating for you. If they need to turn you off course for traffic, they will, but that's the exception, not the norm.

Answer 3

On FSX you have to change the NAV/GPS toggle switch to GPS to follow the preplanned route which is shown in the FMS display. Once you reach your designated airport the ATC will give you vectors to intercept the ILS. At this stage you need to enter the ILS frequency into the NAV1 and switch the toggle switch to NAV. The autopilot will then follow the ILS. Not sure how realistic this is with real life flying!