Well, as I said I haven’t tried to do it myself. Just a thought. LNAV+V is great though!
Aviathor, that’s exactly what I tried and it doesn’t work — neither in the simulator nor in a real G1000. You can’t set the desired altitude.
JasonC, I guess you’re right in that they don’t want you doing it, but why not?
AFAIK, manually setting it to 0.3nm FS sensitivity is the same thing, in terms of lateral guidance accuracy in the final stage of the descent, as the automatic sensitivity increase from 3nm to 1nm to 0.3nm which you get on a database GPS/LNAV approach.
The caveat is that if you fly the whole T-shaped approach with 0.3nm FS manually set, you will likely get some under-damped turn behaviour (e.g. overshoot and oscillation, though it should damp out eventually) on the 90 degree turn. The automatic sensitivity increase which you get on database approaches avoids this issue, by flying the 90 degree turn with a very low proportional gain (unless you have roll steering).
Peter,
The WAAS GPS CDI FSD doesn’t work the way the non WAAS units do. The FSD at the FAF is the lessor of 0.3 NM or 2 degrees. The 2 degree FSD at the threshold is +/- 350 feet.
The G1000/GFC700 FMS is going to use roll steering if the navigation source is GPS. The T concept is pretty much an RNAV one, although it has been applied to an ILS at our airport, KUZA ILS Y RWY 2.
The LNAV+V feature is restricted to RNAV approaches and not available on ground based approaches. More sophisticated FMS systems provide VNAV on ground based approaches using Baro VNAV. I haven’t seen GPS being used for vertical guidance on ground based NPA procedures, but FMS systems with Baro-VNAV for vertical guidance has been used. The Baro-VNAV systems have the advantage of not requiring WAAS for the lateral guidance and they don’t have the issue of not matching the MSL values charted on the approach charts that WAAS GPS vertical navigation has.
Proline 21 gives advisory vertical nav which can be coupled to the autopilot, and even where there is no IAP most airfields have a visual approach coded. This comprises a 5 mile centre fix and the threshold, which is what the OP was suggesting could be manually entered in the G1000. The big advantage is that you don’t have to make user waypoints with all the dangers of sausage fingers causing silly errors. The gotcha is that because it’s Baro Alt based you need the pressure setting to be correct, i.e. if you set the QNH wrong you end up too high or low on short finals.
Can anyone remember how Jeppesen indicate on their approach plates that a non-precision, conventional approach procedure provides Baro VNAV?
Jeppesen does not directly indicate that a conventional approach can utilize Baro VNAV, but it does include a note if the procedure meets certain criteria found in FAA guidance that states “Only authorized operators may use VNAV DA in Lieu of MDA”.
I am quite sure that there are VOR CDFA approaches with Baro-VNAV, and that there is a way this is indicated on the Jeppesen approach plates. I occasionally get vertical guidance on the G1000 on VOR approaches – I cannot remember what approaches.
It is on a DA40. I do not have a very vivid imagination, and I sure I have seen the advisory glide slope during a VOR approach to LFOP. On second thought however, it may have been the GNSS approach. In either case I definitely had the advisory glide slope. It was during a check flight with an instructor.
