Missed Approaches with G1000 & NXi

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Boatguy
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Missed Approaches with G1000 & NXi

Post by Boatguy »

I have NXi, but I think the missed approach waypoints are the same for both the G1000 and G1000NXi.

Many missed approaches have an initial climb and then a route to a holding pattern. A sort of generic procedure might be:

- RW18map
- climb to 1,500'
- climbing right turn to 3,000'
- Direct MAHPY and hold

But the G1000 frequently inserts another waypoint between the MAP and the first official missed approach procedure waypoint. For example, the RNAV GPS 29 at O69, Petaluma, CA, my home airport. The procedure is:

- Climb 3,600'
- Direct XIKIY
- Track 216˚ to HIRUV

But the G1000 inserts "347FT" between the RW29map and XIKIY. The elevation at O69 is 97' so at first I thought this was some sort of minimum altitude AGL they had inserted, 250' in this case. But I looked up others where this sort of waypoint is inserted and there was no consistent AGL. At KJAC it's 6,860' which is 409' AGL. At KEED it's 1,383' which is 400' AGL. The waypoint is certainly not part of the official IAP. So what is the G1000 doing?
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Re: Missed Approaches with G1000 & NXi

Post by jb642DA »

Without seeing your G1000 map and flight plan, this is my best guess - - - - -

A couple of questions for you -
Is 347FT approximately 6 miles from the MAP?
Where is "XIKIY" in relation to "347FT" on your G1000? Slightly after the 347FT point?

A lot of Flight Management systems use "5 character alphanumeric names" for non-charted points (based on a specific point on the ground) where the FMS wants to command the aircraft to do "something".
(ARINC 424 is the "standard" for naming points throughout the world)

My guess is this G1000 "point" is a specific latitude/longitude point, designated as "347FT". The "347" part of the name MAY be used because of the altitude constraint (250AGL +97 field elevation). The first letter in this "name" designates a distance. The "F" would be approx 6 miles from the previous point (the missed approach point).

"F" is the sixth in the alapabet, "H" would be 8 miles and an "N" would be 14 miles,

Below shows the "distance" related to a "letter" -

Image
(this example is for a radial/dme point D090J)

The last letter, "T", could designate "fly-over" (aka: fly "T"hrough) versus "fly-by" the waypoint for the FMS to use. I could make a much better "educated guess" if I saw your G1000 display.

There are good diagrams and descriptions of "fly-over" and "fly-by" points in the recommended FAA manuals below -

FMS history, naming conventions and "fly over" vs "fly through" points - check out the FAA's "ADVANCED AVIONICS HANDBOOK", chapter 3 pdf.
https://www.google.com/url?sa=t&rct=j&q ... 93MaV0PMmJ

or the FAA's "Instrument Procedures Handbook", chapter 6 - https://www.google.com/url?sa=t&rct=j&q ... mZLb11Ezgf
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Re: Missed Approaches with G1000 & NXi

Post by shorton »

I think 347FT is a course to altitude (CA) leg. In other words, when you go missed (hit the TOGA) the FD will command a 7-degree nose up climb along runway centerline until the altitude indicated which will allow a safe turn. In this case on the RNAV 29 at O69, once above 347', the FD will give you commands direct to XIKIY. If you were above 347' when you hit the TOGA, I think the FD would command direct to XIKIY.
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Re: Missed Approaches with G1000 & NXi

Post by Boatguy »

John - that was a very thorough answer, but I don't think it is correct. The waypoint 347FT is shown 1.5nm from the MAP on runway heading at an altitude of 347'. If you climbed at the TERPS 200'/nm minimum you'd be about 1.5nm from the MAP. XIKIY is 5nm from the MAP and 3.5nm from 347FT, also on runway heading.

Scott - That seems more likely, but why the variation in the height of the inserted waypoint at different airports?

Here is a little more data to muddy the water: Apt / DA / Waypoint / altitude relative to DA

O69 (RNAV 29) / 356' / 347' / -9'
KJAC (ILS 19) / 7,500 / 6,860' / - 640'
KADS (ILS 33) / 894' / 1,500' / +606'

These make no sense to me at all.

Full disclosure, I'm getting the waypoint data out of a simulator which theoretically has the current cycle database. Maybe the simulator has bogus data, though I do see these waypoints inserted on my own panel. I'll be at the plane on Monday and get the data directly from my panel.

Standby...
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Re: Missed Approaches with G1000 & NXi

Post by jb642DA »

Thanks Russ -

Like I said, my "best guess" without seeing the G1000 info presented to you.

The "347" in this case may have nothing to do with anything - maybe just be "coincidental" to the airport elevation + 250.
The last two letters are part of the naming "standard".

However, nothing says Garmin has to use the "ICAO standard"!
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Soareyes

Extra Altitude/Waypoint on G1000 Missed Approach

Post by Soareyes »

"But the G1000 inserts "347FT" between the RW29map and XIKIY. The elevation at O69 is 97' so at first I thought this was some sort of minimum altitude AGL they had inserted, 250' in this case. But I looked up others where this sort of waypoint is inserted and there was no consistent AGL. At KJAC it's 6,860' which is 409' AGL. At KEED it's 1,383' which is 400' AGL. The waypoint is certainly not part of the official IAP. So what is the G1000 doing?"

Scott has it exactly right. Garmin starting adding these altitudes to missed approach procedures on the G1000 a few years ago. It is a "Climb straight, don't turn to the first waypoint on the procedure until after you reach this height" altitude. From the G1000 NXi Pilot's Guide:

"In this missed approach procedure, the altitude immediately following the MAP is
not part of the published procedure. It is simply a Course to Altitude (CA) leg which guides the aircraft along
the runway centerline until the altitude required to safely make the first turn toward the MAHP is exceeded.
This altitude is provided by the navigation database, and may be below, equal to, or above the published
minimums for this approach.' ...'In some missed approach procedures this Course to Altitude leg may be part of the published procedure.
For example, a procedure may dictate a climb to 5,500 feet, then turn left and proceed to the Missed Approach
Hold Point (MAHP). In this case, the altitude would appear in the list of waypoints as ‘5500ft’. Again, if the
aircraft altitude is lower than the prescribed altitude, a direct-to is established on a Course to Altitude leg
when the missed approach procedure is activated."
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Re: Missed Approaches with G1000 & NXi

Post by Boatguy »

Thank you Scott and Soareyes. My bad for not finding that in the manual.

I have to say I'm surprised that Garmin is pre-empting the TERPS to decide what is safe and inserting waypoints into the official procedure. When they say the altitude is provided by the "navigation database", I'm not sure who's database they are referencing. They say the inserted point may be above or below the minimums which also doesn't make a lot of sense. At O69 it's below the minimum and at KEED it's at the minimum. Why insert a waypoint at or below the minimums?

In any case the mystery is cleared up and my thanks to Scott and Soareyes.
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Re: Missed Approaches with G1000 & NXi

Post by Paul »

I may be wrong about this but I think I read somewhere that the reason for these waypoints is to prevent a scenario, particularly when you fly a coupled missed, where you hit the GA button and then quickly hit the NAV button. Without a climb straight ahead waypoint, the autopilot or FD may start a turn too early and send you into say, the control tower. This situation can be made even worse if you start your go around early. Imagine an approach where the first part of the missed is a climbing left turn to a waypoint. A mile away you decide to go missed and hit NAV. Without that waypoint, the autopilot would start turning before the runway. The fact the extra waypoint has an altitude associated with it should not matter because the bugged altitude that the auto pilot will fly should be the missed altitude from the plate that you enter.
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Re: Missed Approaches with G1000 & NXi

Post by Boatguy »

Paul is correct. The AIM is clear that the missed approach procedure begins at the MAP. If the pilot begins the missed before the MAP, the lateral instruction of the procedure must be followed to the MAP. I guess the extra waypoint reinforces that.
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