Vector to final on RNAV approach with the Intermediate and final segments are not aligned

Question

Consider the RNAV 30 approach to C83 (Byron, CA),

On a recent training flight requesting vectors for the approach, ATC pointed us to the MOVDD IF before cutting us loose (informing us that we would be getting a vector to that fix). The segment between here and the FAF is 11 degrees off from the final segment. On a GTN650 at least (and I assume other similar Garmin devices), selecting “Vectors” as the approach method gives you the FAF line with your deviation from it & sequences from the FAF. This seems not correct for flying this particular approach. The best my CFI & I could come up with was to enter the approach as being flown from the IAF (SMONE) then select “Direct to MOVDD” sometime before reaching it (such as when ATC gives the last turn), after which the GPS will sequence to the intermediate-to-final segment. But this seems non-standard. What do others do in this situation?

Answer 1

Since most fatal accidents are during approach, it is important to maintain 100% compliance with the procedure and have a clear understanding of what your FMS will do with different modes.

There is an important Garmin / FMS distinction between:

1. Selecting "Activate Approach" mode when navigating to a fix leading to an approach sequence, and;

2. Navigating directly to the FAF via ATC vectors by selecting "Vectors to Final" ("VTF") mode.

If you select Vectors to Final in G1000 or G3000 (likely similar to your G650), the following things happen (from memory, I may have missed a few):

1. The waypoints in the flight plan are bypassed (but remain inactive in the plan and available to re-navigate direct to) and the FAF is made active;

2. Approach mode is engaged (which increases needle sensitivity);

3. If you have a non-GPS approach loaded, the frequency for that approach is made active and the needles switch to the relevant indication (green needles for ILS for example);

4. If you are navigating to a GPS waypoint, the FMS turns off lateral guidance and engages roll-mode (if you are in Heading mode, that mode is maintained);

5. The HSI Bearing Needle is set to the final approach course (or outbound course for a back course approach);

6. A graphical magenta line representing an extension of the line between the touchdown zone and the FAF is drawn on the map.

It would be unusual to use VTF (in IFR conditions) without being under some form of ATC guidance on vectors and terrain clearance - Hence 'Vectors' to Final. The use for VTF mode is usually when the pilot receives a clearance as follows:

ATC: N188L, six miles from BABPI, turn right heading 280, maintain two thousand six hundred until established on final approach course, cleared RNAV runway 30 approach Byron Airport.
Pilot: Right turn 280, two thousand six hundred until established, cleared RNAV 30 approach, 88L.

(The italicized sections are meaningful; look them up in the Pilot Controller Glossary)

At that point (assuming already at 2600), the pilot

1. Affirms the correct approach is loaded in the FMS flight plan;
2. Dials in 280º on the heading bug;
3. Engages heading mode, and;
4. selects Vectors to Final and the Garmin will then auto engage the approach from the FAF inbound. (Since this is a LPV approach, the Garmin will also intercept the vertical flight path.)

A contrary but common clearance might also be:

ATC: N188L, cleared direct MOVDD, cross MOVDD at or above three thousand, cleared RNAV runway 30 approach Byron Airport.
Pilot: Direct MOVDD, MOVDD at or above three thousand, cleared RNAV 30 approach, 88L.

In this case, there is a distinctly different FMS sequence:

1. Affirm the correct approach is loaded in the FMS flight plan;
2. Select MOVDD in the flight plan (this will be either an IAF or an IF);
3. Select Direct To - Enter - Enter to make active;
4. Select FMS mode (if not already selected and skipping the part to make sure the ship does not jump uncomfortably towards MOVDD);
5. Engage Approach Mode;
6. The Garmin will now auto sequence the approach including auto selecting green needles to fly an ILS or VOR if required. The Garmin will also intercept the vertical flight path if available.

You state in your question ATC pointed us to the MOVDD IF before cutting us loose (informing us that we would be getting a vector to that fix)

So what you do is:

1. Enter Direct To MOVDD and fly that course;
2. Select Activate Approach when you are cleared to fly that approach;
3. If ATC gives you a vector (perhaps because ATC does not want you to go straight there) then you enter heading mode and use the bug for that vector. Reset Direct To when ATC stops vectoring you.
4. Even if you receive a vector, you continue to have MOVDD as the active waypoint and you do not engage VTF unless you receive a clearance and a vector related to that clearance with the intent of you ending up on the final approach course near the FAF or a linear extension of the final approach course.

For illustration, consider the approach to KEGE (below, with the Vectors To Final magenta line drawn.

If you were to select VTF well outside of the IAF for this approach (and you were not under ATC POSITIVE CONTROL) there is a high risk that you would hit the 11,200 foot mountain just 7 miles from the FAF on the magenta line.

If VTF is engaged at a time when the pilot does not understand the sequence or limitations, BAD THINGS CAN HAPPEN! The FMS itself does not maintain terrain clearance for you.

Answer 2

You stated ATC indicated they will give you vectors to the IF and not vectors to final (VTF). Why would you select VTF when that is not what ATC is doing? It's a rhetorical question but hopefully designed to allow you to realize that VTF is, in my opinion, the non-standard method.

I have flown lots of different GPS/FMS installations. They all have VTF feature. Some called it activate approach while other call it VTF. All of these will provide guidance to the final approach capture fix (FACF) which is typically the waypoint in front of the FAF. Some approaches don't have an intermediate fix outside the FAF and those may have a computer navigational fix (CNF) that the GPS / FMS uses to align the final approach course. All CNF waypoints are surrounded by square brackets [CFBTF] as depicted on KICT ILS 01L. You will only see the CNF waypoint if you do not select a transition on the GPS / FMS.

Others approaches, like the one you mentioned have multiple waypoints outside the FAF. In this case, you will not see any waypoints outside the FACF (in this case, MOVDD). If you were vectored to one of those you will need to select SMONE as the transition and let the FMS / GPS auto-sequence after you pass it.