Peter,
The split of the display has no impact on if it requires an STC. If it requires TSO C113, then it needs the STC, This unit is no different than an Aspen, which is also offered in a similar configuration as a backup unit.
Sorry but I disagree. I think you meant "no effect on the pitot values". My aircraft has two static ports, one on each side of the cowling. In a strong crosswind, there is increased pressure on the windward port and decreased pressure on the other port. If the windward port is clogged, a higher altitude will be displayed.
A plane in non-yawed flight (ball in the centre) is not aware of wind - crosswind, headwind, tailwind, etc.
Wind is just the movement of air over the earth's surface. A plane knows nothing about the wind. A plane flies totally relative to its own frame of reference which is the air. If the air happens to be moving also (called "wind") that will affect the plane' progress over the earth's surface (ground speed, etc).
Back to that backup instrument, I think the reason they have split it into two must be to avoid the need for an STC, which is bizzare. It makes it a funny shape which won't fit into many places.
The Garmin GPSMAP 695 does not have any integrity checking and can be well off altitude or position without notifying the pilot
Doesn't it receive WAAS/EGNOS?
That's pretty good normally. I have a G496 which picks up EGNOS and that reads the altitude of some known place to within ~ 10ft.
But my old KLN94 is not much worse. 20-30ft is normal.
I would certainly be very wary of the altimeter reading if the GPS was say a few hundred feet off it, in IMC. In that case I would probably go somewhere with an ILS.
Achimha,
Sorry, that is not how physics of an aircraft in a free stream of moving air works. The reason for static ports on both sides of the aircraft is to account for differences caused by skids and slips and momentary turbulence. The direction of the relative wind is not affected by a crosswind once an aircraft has accelerated into the free stream. It is momentarily affected by transient changes (turbulence), but not by a steady wind.
A crosswind will have no effect on the static port values. A slip or skid would have the effect that you suggest, but normally that is a transient effect, unless you are continuously flying in a slip or skid, which would not be the case in IMC.
Sorry but I disagree. I think you meant "no effect on the pitot values". My aircraft has two static ports, one on each side of the cowling. In a strong crosswind, there is increased pressure on the windward port and decreased pressure on the other port. If the windward port is clogged, a higher altitude will be displayed.
The Garmin GPSMAP 695 does not have any integrity checking and can be well off altitude or position without notifying the pilot. In the US it may be used for situational awareness, but is not approved for IFR.
The GNS430W can display the same value. If I see a difference between GPS altitude and barometric altitude that is significant, I know that something is not right. It is therefore a very valuable indicator. Think about my above experience with the clogged port and image IMC down the runway.
achimha said:
No but I keep an eye on it. I mentioned it before: I had a clogged static port and performed an IFR approach in a strong cross wind situation. This made all my altimeters (glass cockpit, steam gauge, transponder, autopilot) over read by a large margin, i.e. I was much lower than I should have been. The reason is the cross wind -- there are two ports on each side of the air craft and with a cross wind you have increased pressure on the wind facing side and lower pressure on the other side with the combined pressure being the "normal one". If one side is clogged, you will get wrong readings.
A crosswind will have no effect on the static port values. A slip or skid would have the effect that you suggest, but normally that is a transient effect, unless you are continuously flying in a slip or skid, which would not be the case in IMC.
The Garmin GPSMAP 695 does not have any integrity checking and can be well off altitude or position without notifying the pilot. In the US it may be used for situational awareness, but is not approved for IFR.
Are you saying that you rely on altitude readings given by your GPS receiver rather than the indications of your altimeter to determine reaching a decision height during a precision approach?!
No but I keep an eye on it. I mentioned it before: I had a clogged static port and performed an IFR approach in a strong cross wind situation. This made all my altimeters (glass cockpit, steam gauge, transponder, autopilot) over read by a large margin, i.e. I was much lower than I should have been. The reason is the cross wind -- there are two ports on each side of the air craft and with a cross wind you have increased pressure on the wind facing side and lower pressure on the other side with the combined pressure being the "normal one". If one side is clogged, you will get wrong readings.
I now monitor the GPS altitude and I trust it more than the static port. When they disagree, I would engage the alternate static switch, taking the pressure from the cabin.
That is a very interesting statement. I hope you don't really mean it, either part, suggesting that one uses the GPS altitude to establish the DA/MDA or that one would not pay close attention to terrain warnings.
No, I meant the opposite. One is used to getting terrain warnings during approach (at least I am because my Garmin 695 is wired up to the intercom) so one gets used to them. When my DA is 200ft and my static system tells me I'm at 250ft while my GPS tells me I'm at 180ft, I tend to believe my GPS and take immediate action.
achimha said:
However, it is the best / safest indicator during approaches when it comes to DH/MDA, especially since one is used to terrain warnings during approach and tends to not pay close attention.
That is a very interesting statement. I hope you don't really mean it, either part, suggesting that one uses the GPS altitude to establish the DA/MDA or that one would not pay close attention to terrain warnings.
achimha said:
.... it (the altitude indicated by a GPS receiver) is the best / safest indicator during approaches when it comes to DH/MDA....
Are you saying that you rely on altitude readings given by your GPS receiver rather than the indications of your altimeter to determine reaching a decision height during a precision approach?!
one cannot follow the actual figure to comply with ATC instructions, because one isn't going to get the separation they expect
However, it is the best / safest indicator during approaches when it comes to DH/MDA, especially since one is used to terrain warnings during approach and tends to not pay close attention.
Yes; GPS altitude is very accurate, when the GPS is getting a decent fix. With EGNOS it is usually within about 10ft.
The problem is that it is often different from what the altimeter says even if you have the right QNH set, because the altimeter measures pressure and that is affected by temperature. And probably by humidity, for all I know...
If you wanted to fly just above a summit of some mountain which is charted (on a modern chart!) at say 15123ft, there is no point in doing with with an altimeter because you will be doing well to be within a few hundred feet. It's amazing how big the errors are at any altitude.
I certainly use GPS altitude as a gross error check on the altimeter but one cannot follow the actual figure to comply with ATC instructions, because one isn't going to get the separation they expect, and also the transponder (which measures pressure altitude) will be reading something different...
