How’s that?
I was referring to having somebody watch the SV, not to 0-0 approaches 
It’s true that the GTN750 website doesn’t mention SV.
So, back to the original Q – do any of the terrain databases actually expire?
So, back to the original Q – do any of the terrain databases actually expire?
I only know about the Honeywell EGPWS terrain database. They expire after one year. It will continue to work normally (as does every FMS that I have come across) after database expiry, but French SAFA inspectors will keep you on the ground until someone has updated the database.
Yes, I do believe that, in an emergency, syn vis could be sufficient to get you into a VFR field in a very low cloudbase/fog or to deal with the scenario…
Certainly. But in an emergency, your options are “almost certain death” or “maybe getting away by doing something unusual”. A big problem with this single-engine synthetic vision stuff is that everything comes from a single source only. One gyro, one GPS, one altimeter input, one airspeed input. No comparison monitor, no nothing. Maybe your gyro starts to drift during the last 100 feet of your zero/zero SV approach and you come out with 30 degrees of bank and 10 degrees nose down attitude. This will be a very interesting exercise in “recovery from unusual attitudes”.
“I already have what Garmin call “certified TAWS”. That is just the same thing, maybe with some aircraft performance specific tweaks, which you get in the old G496. The non-certified TAWS doesn’t give you voice warnings, so is useless – like car satnav without voice guidance. But they still charge plenty for “certified TAWS”.”
Peter,
When I last looked TAWS-B was a $7000 option on the GTNs.
Without that you will get no visual terrain alerts and no audio warnings.
All you get is the orange/red appear on the map.
I had exchanged emails with the Garmins UK manager about them offering TAWS-C at a lower price.
He did try bless him but I think hit a stone wall.
So we bought a £500 Aera and plugged that into the intercom for TAWS audio warnings.
Daft ain’t it.
Certainly. But in an emergency, your options are “almost certain death” or “maybe getting away by doing something unusual”. A big problem with this single-engine synthetic vision stuff is that everything comes from a single source only. One gyro, one GPS, one altimeter input, one airspeed input. No comparison monitor, no nothing. Maybe your gyro starts to drift during the last 100 feet of your zero/zero SV approach and you come out with 30 degrees of bank and 10 degrees nose down attitude. This will be a very interesting exercise in “recovery from unusual attitudes”.
what next, I was agreeing with you! It is only a dire emergency thing – even though I do have two of each item you mention it doesn’t matter. I have one set of eyes. There is nowhere I need to be that needs that sort of risk taking.
but French SAFA inspectors will keep you on the ground until someone has updated the database
Presumably because it is in your MEL? That wouldn’t apply to private ops in a typical light GA type.
what next
A big problem with this single-engine synthetic vision stuff is that everything comes from a single source only.
That depends. If you use an Aspen 2500 setup, you actually do have 2 totally independent AHRS systems as well as totally interchangable screens. I’d say that allows for quite a lot of redundancy. Both boxes on top of that have batteries which will continue to display for about 40 minutes.
Re the SV option:
Single engine IFR becomes a LOT safer with it, particularly with regards to the dreaded engine out in IMC. SV will give you a fairly accurate display of the terrain and allows you to glide into valleys you’d normally not see. I have heard of several documented cases where SV equipped airplanes managed to get to a VFR mountain airfield in the US with reduced engine performance and in one of the last seminars I went to someone related a case where a SEP over the Rockies managed to negotiate his way into a valley where he became visual at 500 ft above ground and could land on a private field without any damage to the airplane or himself.
I’m seriously looking into that option when I go for my Aspen later this year. It will be a single screen for the moment for budget constraints (will need to install an AP at the same time) but I consider SV a very valuable addon to this already very versatile instrument.
Clearly, SVT is NO reason to fly IMC approaches into places where there are no legal approaches. But it can save your life if you will get down whether you want it or not.
Single engine IFR becomes a LOT safer with it, particularly with regards to the dreaded engine out in IMC. SV will give you a fairly accurate display of the terrain and allows you to glide into valleys you’d normally not see. I have heard of several documented cases where SV equipped airplanes managed to get to a VFR mountain airfield in the US with reduced engine performance and in one of the last seminars I went to someone related a case where a SEP over the Rockies managed to negotiate his way into a valley where he became visual at 500 ft above ground and could land on a private field without any damage to the airplane or himself.
This is indeed a very serious case for SV, but I am juxtaposing it to a moving-map display where we take terrain elevations and superimpose a safe-glide cone onto it, getting a moving map of what we can reach and what we cannot, like this:
(Sorry for the psychedelic colours, it’s just a crude handmade example).
In my naïve opinion, I’d rather have a moving map – what are the advantages of SV over it?
I flew self made approaches to grass runways in low visibility settings (e.g. cloudbase 300 feet) but not the zero/zero stuff. I would know the strip and obstacles and fly a stable OBS approach into it with no problems and seeing the obstacles, terrain and runway in front of me. However, I stopped doing this as I consider it way too much risk as the area is not surveyed and could hit an obstacle that is not in my database or on the chart easily. In any case, the synthetic vision helps there to “see” the runway before it becomes visual in the last moment. Also, the dimensions are quite accurate as you approach the runway. If you fly the Garmin Perspective, it is not a choice of either the synthetic vision or the moving map. You have both in front of you on the PFD and MFD. Was it wise for me to do these approaches? No, certainly not. That is why I stopped doing them.
When flying in low visibility settings (e.g. when its snowing) and established on the ILS, the synthetic vision tells you where to look for the runway. OK, you can ‘calculate’ it based on the crosswind and your distance from the runway, but the SV makes it so easy to see and spot it. Then, the SV is GPS based while the ILS on which you are flying is not based on the same source, so it is a confirmation that you are on the right track.
If you fly the Garmin Perspective, it is not a choice of either the synthetic vision or the moving map. You have both in front of you on the PFD and MFD.
Does Garmin offer a moving map of heights over terrain predicted for glide with engine off, or just a moving map of elevations with terrain warnings for the current flight path (à la Garmin 396)? It’s the former that I’m talking about.
Ultranomad, I am not getting the point. Why talk about the engine failing glide path in a Cirrus if you have the chute to pull. I am seeing the SV as quite a valuable tool next to other means such as the needles on the ILS e.g. Remember, here and there we loose experienced (IR rated) friends flying into mountains, which they would have most likely avoided if they had SV. Then, if my front screen is all iced up, where do I look? Only at the steam pipe needles or do I use the GPS based synthetic vision as well.
Yes, there is no comparison really.
