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Synthetic Vision options, and marginal IFR

I personally LOVE synthetic vision. It is a great extra safety feature, but can not stand alone. I have never encountered that a runway I was approaching and that was in the database was somewhere else. The centerline is exactly there where the synthetic vision depicts it. I am aware of the possibility of GPS outages and the possibility of some offset, but as for seeing the runway there in front of you on the screen and compared to where it actually is when you are there, it has so far never failed me.

Look at the Couchevel approach. The runway is there and once on the runway, the centerline is exactly there where you would expect it to be.


It is another story when you use synthetic vision to avoid mountains and terrain. The general contour is visible, but not the exact shape of the mountains. So, I personally believe it helps you to stay safe when used in combination with other methods but I would not just go over a cliff in IMC based on synthetic vision. No way. However, if you are on the ILS inbound to Chambery in heavy IMC weather, the picture of the lake below you (Lac du Bourget) on the SynVis and the contours of the mountains around you gives an extra confirmation that you are ok and would also give you a better protection and situational awareness when then having to do a missed approach.



The pictures above are taken while flying around Massif du Mont-Blanc. You can easily compare the synvis picture with what is outside. And I would not do that kind of flying in IMC around there, but it definitely helps.

The infrared camera in the Cirrus can be of help to spot the runway in low visibility procedures as long as the runway lights are hot and not LED lights. During taxi it can help you spot people and animals on taxiways or runways, but I personally have found it of no use to spot mountains or terrain in IMC conditions.

EDLE, Netherlands

Airborne_Again wrote:

Do you mean that Terrain Safe doesn’t work in other chart formats?

It works, but the opaque or semi-opaque trees layer covers it. So, for now, if you want to use something other than ‘SkyDemon 2’ and Terrain Safe, I’d recommend turning ‘trees’ off.

PetitCessnaVoyageur wrote:

Maybe not the place to ask, but what seems to you the most effective, in terms of avoiding CFIT: Synthetic Vision or TAWS ?

Altitude.

TAWS is a collective term by the FAA which covers GPWS and EGPWS. It can be class A, B or C. My G1000 is a class B. I don’t view SV as a terrain avoidance tool. But it can be a useful representation of terrain data.

Wikipedia sets out some summary of what each class involves: https://en.wikipedia.org/wiki/Terrain_awareness_and_warning_system

EGTK Oxford

Another personal view is that SkyDemon does help in staying clear of terrain. Of course, you plan ahead using all the means you have, check the plates, MSA etc. But once if flight and in the last phase of flight going from IFR to VFR for a VFR arrival, SD can be of great help and gives you additional awareness. Also, I have had one situation where I placed the iPad on the windshield straight in the sun. Then the iPad would overheat. Placing it somewhere else, I have never had that happening to me, even if the outside temperature was over 35 degrees as when flying through South Sudan. It would simply continue to work. I used to have an external GPS receiver that would be linked to the iPad, but for the last 2 years I just use the built-in GPS receiver and it never failed me so far. As a backup I have my iPhone 6s with the same apps and up-to-date SD.

Oh: and I have had the G430W fail me once in flight in IMC due to the antenna connector going broke while flying at night to Vienna International. I was so glad I had the iPad there as a backup with the approach plates georeferenced. The ILS still worked as the GPS antenna was broken, but if the G430 doesn’t know your position, a lot of stuff will stop to work. It won’t know nearby stations. So it helps to have something else as a backup.

Also, I have had a Garmin Perspective MFD going black while in busy airspace inbound Rotterdam (also at night). You bet I was happy to have the iPad there as an alternative means. Also got twice an alternator failure where the battery would be dead within 20 minutes (or faster) where the G430 would go dead. Thank God there is such a thing as the iPad with all these great apps :-)

EDLE, Netherlands

what seems to you the most effective, in terms of avoiding CFIT: Synthetic Vision or TAWS ?

I have never flown with SV but have had TAWS (the Garmin 496, wired to the intercom) for 11 years. At the time at least, it was widely believed that the database is identical to the certified TAWS option in the GNS530 except for some extra work around airports having been done in the certified version.

The G496 predicts your current trajectory for 2 mins at the current GS and warns if there is terrain. I have tested it at various places, including flying towards a 500ft cliff at 400ft and then at 600ft and that was spot on. Plus it gets tested all the time during normal departures and arrivals.

Once or twice it generated seemingly totally spurious warnings.

But I would say it would totally protect you from a CFIT – provided that you don’t try to do one near an airport because the warnings are progressively disabled (except the “FIVE HUNDRED” one which seems to always operate, anywhere) on an IAP or a visual approach.

The problem with it is that when there are mountains around, it is warning all the time, so would be difficult to use in IMC. However it does pop up a picture of the offending terrain so if you are in a real hurry and there is room to go elsewhere, you could just look at that and turn away. But the resolution is way too low to go flying between mountain peaks. For that you would need a really great display with very good resolution, shadowing, etc.

On the wider topic, I am surprised nobody seems to have done an open source project which downloads google maps tiles (if necessary very slowly, to make it look like lots of people browsing the site, so google doesn’t block it) and presents the data in an SV app on a tablet. The technology existed almost 20 years ago, in the oldest flight sims.

The reason I make the point is nothing is made to allow flight below MSA when not visual.

I agree. However at least one legitimate use is in an engine out emergency above an overcast or at night.

Administrator
Shoreham EGKA, United Kingdom

Regarding comparing flight simulation terrain (let alone scenery) with what is needed for virtual terrain in an avionic application, there is a lot of things to be considered.

In Flight Simulation, particularly today, the representation of terrain must be much better than in any SVT application, because the purpose is the opposite. On a FS terrain, you ideally want to get sufficient grid points to actually be able to land and take off from that grid without artificial help, e.g. flatten polygons or likewise. Very few achieve that. The second bit is, that the visual representation is desired to be such, that it eventually replaces the outside view altogether in a photorealistic form, ideally without the use of texture. Not many achieve this so far, and if so then not in a huge coverage.

The best package for this kind of thing (MS Flight Sim and Prepare 3d) is FS Global Ultimate New Generation and that is a pure altitude grid. World wide, it is 80 gigabyte. The resolution however is pretty much ultimate and a lot of work went into it to make it look this way, it is not just raw data.

For SVT, the main goal is to actually AVOID terrain, not to hit it. So you need a lot less terrain features, but you are looking for extremes like mountian tops, valley bottoms. Aspen uses three arc-second terrain data. Even the most rudimentary of grids in a sim today use 1 arc second, which is much higher, high fidelity meshes go even further. With each higher level of detail, the amount of data grows exponentially. But for this kind of application, you do not need something even approaching 4 meter grids as you are not trying to show a post card picture but a approximation of the terrain. So 3 arc seconds in our latitudes are approximately 90 meters, whereas the highest fidelity flight simulation grids go down to below ONE meter (most are 4.75m).

That is why comparing a world wide Garmin DB with things like the world wide scenery of Xplane or FS Global is totally useless, as the requirements are very different.

To avoid terrain, 3 arc seconds are more than adequate, provided that they are enhanced with peak altitudes and obstacle databases. That is what I understand these db’s are. The goal is to give you terrain clearance, not to enable terrain following like e.g. for a Tornado or a Cruise Missile.

Would the mountain the TB20 came to grief at be there? Most probably yes, it would appear rounded at the top however, which is not really a problem as long as the peak altitude is at the same spot.

In the Garmin 695, terrain avoidance looks like this.

It gives a pretty good representation of the surrounding terrain and of the valleys available to descend into if the need arises. I’d say in case of cases (engine out over the alps in IMC as the worst example) it would be a darn sight better than nothing but also not as good SVT. But it would definitly help finding low ground in an emergency. It should, in both cases, not be used to do illegal IMC operations, that is self understanding.

LSZH(work) LSZF (GA base), Switzerland

Peter wrote:

That all sounds rather theoretical, LeSving. Is there a product out there which uses this “free data” to generate an SV presentation usable in flight?

Who knows? Official and updated data, is still official and updated if it is open and free. There is no difference with this and other data like weather and notams. There is a EU site, INSPIRE where the very patient can find everything available in EU and EEC. Lots of places with such data, Germany, Austria, France etc etc.

I know that EasyVFR use NASA data 500*500m, sampled from higher resolution and is formatted to give “the best combination of safety and performance on devices with limited computer power” according to their documentation.

As far as I am concerned, I would much rather have some real and accurate Norwegian/Swedish open and free data that is based on real world measurements, maps and laser scans from airplanes, than some NASA space shuttle nonsense, that is only a scan taken from space, ages ago.

I tried to find what SD and Garmin uses, but couldn’t find anything.

The elephant is the circulation
ENVA ENOP ENMO, Norway

This is from the google terrain data I run on a tablet, under Oziexplorer

You can overlay airports, roads, etc, but I didn’t bother. Well, it looks like there are roads in the valley!

Here is another one

Administrator
Shoreham EGKA, United Kingdom

Posters here keep referring to the data resolution of the map. The resolution of the geoid is only one issue however. It doesn’t really matter what the resolution of the terrain is, the gps receiver also needs to know exactly where it is. Talking about tablets, that is.

Horizontally, without correction, most of the simpler GPS receivers have a standard of accuracy of 15m in 95% of all cases, if they don’t have any correction. Meaning, in 95% you get an at least 15m exact position (mostly better), but in 5% of the cases you get anything from 0 to wherever. Some devices do, some don’t have assisted signal correction, which is usually a differential data signal from a standard fixed location with known coordinates, received via wifi (that’s why the iPhone tells you it can locate you more precisely with the Wifi on).
In that case they call it assisted gps and you can have even 2m. Normally, the ephemeris data (the orbital track data from the satellites) are valid for apprx. 4 hrs, so once you got a position fix (i.e. at the airport, or at home) it usually remains valid, and you get a very precise information for the flight. As long as there is a clear view to the satellites. Which is why so many people use it. It’s great. Just wonderful.

The altitude errors, however, of the gps devices are more prominent, i.e. vertical accuracy is apprx 2-3 times less exact than horizontally, so the error can be 30-50m quite easily. iPads do not have any WAAS / EGNOS capability (some Android devices do), only the differential correction provided by Wifi I mentioned above. So, not available in your cockpit. There, you need an azimut of 40-55°, I believe, to achieve a good satellite signal, which you won’t if you are below the higher peaks around you, and you need to be able to differentiate signals down to -190db (not just -130 or so in a tablet) which you won’t if there are mountains around you. At least not inside a cockpit. And, the tablet gps apps don’t realize they’re getting incorrect data. So, in or close to the mountains you have bad reception, no error correction, no warning. It can be right – but it can very wrong.

Forgive me for repeating this, but I guess it’s important to say. In order to use SV in any way for flight ops, you definitely need an aviation grade GPS device, with antenna, good signal reception, and the proper altitude correction.

Some of the posters here provide fancy images of yellow and red terrain and it looks as if you could basically fly through mountains with these devices. Let these apps not fool you, they’re far from accurate enough to bet your life on them.

Last Edited by EuroFlyer at 01 Dec 15:55
Safe landings !
EDLN, Germany

This is terrain on the G1000 MFD. It’s a great tool when flying in the mountains.
Most Garmin GNS units have terrain and obstacle data. I always switch it on when flying in IMC.
This should be tought to any PPL student rather than fiddling around with a E6B…

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