It can also be interesting for providing situational awareness during a visual approach as it creates a big magenta extended runway centreline.
I was thinking just that, but obviously it will work only if there is a published GPS/RNAV approach.
For all other cases the OBS mode has to be used, and I can't see any difference between the official VTF mode, and using OBS with a manually selected 0.3nm FS.
Maybe a refusal to display the approach if a RAIM check fails, might be one difference?
I am a great fan of the OBS mode, and always set it up as an extra reference for an ILS.
Years ago I looked at replacing the KLN94 with a GNS430/W but stopped when I found the KMD550 would not display the two extended centrelines in that mode, because King annunciate the OBS mode in the GPS data, whereas Garmin don't (they use a wire). This then led to looking at some Avidyne MFD but I could not get Avidyne to confirm the functionality. Also at least some of the Avidyne MFDs have poor sunlight readability. Consequently I am not changing the GPS until PRNAV is mandated for enroute airspace...
Will work on overlay approaches as well eg VOR/NDB or ILS. And the difference I think is that it will be aligned to the inbound track of the approach not an ARP or somesuch. Obviously you can do it with the right waypoint and OBS mode.
I always load an approach if one exists and if I don't need the actual approach activate VTF to give the SA.
OBS mode was integral to flying the early GPS units, although you had to always switch to Leg mode (or equivalent) prior to 2 NM from the FAF. With the GNS430 and later units, OBS mode is not used on an approach and many pilots don't know for what OBS mode is used. Although you can use a direct-to a fix in the approach flightplan, it must be a fix other than the FAF, which means you must fly a leg that ends at the FAF, activate the final approach leg, or use VTF, otherwise the GPS will display an error message to the effect that the approach is cancelled. We teach pilots to avoid using VTF because it erases the approach flightplan waypoints except the FAF and the MAP. VTF will extend a magenta line 30 NM from the FAF along the course aligned with the IF - FAF direction. Most of the time this is the same as the final approach course, but here in the US, there can be a turn at the FAF of up to 30 degrees. I had to miss an approach in such a case where the controller insisted that I fly the extended centerline of the final approach course, but the G1000 would not permit it. Technically, I found a way to do it later by trying various techniques on the simulator, but I would not expect a pilot to discover it while in IMC flight. Even so, it is not following the approach chart which violates the regulations.
Even so, it is not following the approach chart which violates the regulations.
??? Every instruction you get from a controller other than "cleared standard xyz approach" means that you will not be following the approach chart. How would that be a violation of any regulation?
Vectors to final is a misnomer when there is a turn at the FAF from the intermediate leg. The extended final approach course in this case is not part of the approach, as it would normally be true when the intermediate course is an extension of the final approach course. The reason for the turn may be due to airspace or terrain/obstacle considerations. I was cleared for the approach at an altitude 1000 feet above the normal altitude expected at the FAF. As I was not on a depicted portion of the approach, I could not initiate the descent until reaching the FAF, where I would be on a depicted portion of the procedure, which would make the approach descent gradient beyond the maximum permitted. Furthermore, the GPS indicated that the approach was cancelled as I attempted to generate a course that the controller wanted. The controller could vector me to the intermediate leg in this case, which is what the approach chart called for and the GPS would offer this guidance with VTF, but he did not.
This was resolved by me not accepting the clearance and declaring a missed approach. The controller was in training and the supervisor came on and permitted me to fly the approach as depicted. I followed up and sent the supervisor a simulation of what I was seeing in the cockpit. This was a military facility and when this was discussed at the next ATPAC meeting, the Naval Officer who attends the meetings followed up with the facility. I made a recommendation that guidance be added to the controller manual to explain that when there is a turn at the FAF, that different terminology be used and that vectors only be made to join the intermediate segment. The consensus at the meeting was that this was a one off situation and that controllers understood that vectors to final in this case meant vectors to the intermediate leg. I am not convinced, but that is where it was left.
That seems to be the same problem as being vectored to an ILS too close so a glideslope intercept becomes impossible.
I've had a few of those, around Europe.
However I suspect a contributory factor in them may have been my tendency to moderate the rate of descent when given a descent (say -500fpm when that looks more than adequate), whereas ATC may have been expecting -2000fpm.
Look at this one:
As you can see, there is a dogleg at PETIT (the final approach fix). Therefore, if you don't activate vectors to final (as happened to me because I didn't manage to do so with the KLN94), in case of ATC vectoring, you will have no direct clue as to when you intercept final...
But ATC did give me vectors. How is this supposed to work?
[edited to put a blank line before the image]
In that case I would think VTF activates the FAF to MAPT leg extended. Without VTF, the GPS will activate the relevant leg it thinks you are going to and if you intercept the IF to FAF leg then it would allow you to capture that. I need to dig out the full G1000 manual to check on this though - I may fly it in the simulator and see what it does.
As I was not on a depicted portion of the approach, I could not initiate the descent until reaching the FAF...
... Unless the controller, based on his MRVA (minimum radar vectoring altitude) chart, allows you to descend to the FAF altitude so that you can follow the final approach path from there. This is how they do it in our part of the world. Sometimes they will also vector you to a point "inside" of the FAF at a lower altitude. Before they are allowed to do that, they have to ask you first if you can accept an X mile final.
And I was going to ask what the MSA was vs the altitude you were at.
