Once Adam gets his plane back in the air, I suppose he may regularly fly above 18000 feet since it is a pressurized turboprop… Or did I miss something?
Aviathor wrote:
Just to clarify, in case it is necessary, transition altitudes in Europe are generally 3000-6000 feet and depend on the terminal area and QNH.In the US it is 18000 feet everywhere.
I understood, but thanks for making that context clear.
Silvaire wrote:
I wonder how how often Adam flies above 18,000 ft transition altitude?
Just to clarify, in case it is necessary, transition altitudes in Europe are generally 3000-6000 feet and depend on the terminal area and QNH.
In the US it is 18000 feet everywhere.
Martin wrote:
I guess I’m slow but you’re using 1013 hPa when above transition level as well.
I wonder how how often Adam flies above 18,000 ft transition altitude? 99.9% of US GA operations (I’m guessing) are conducted below transition altitude, with an altimeter setting different than the Mode C encoder.
I have never flown above TA and likely never will.
AdamFrisch wrote:
No, the altitude on the transponder is corrected on the radar with the actual local QNH. It sends out in 1013 Hpa. Don’t mess with that.
I guess I’m slow but you’re using 1013 hPa when above transition level as well. I don’t see a reason why would ATC want to see the actual altitude instead of flight level (however, I’m not a controller). And I doubt TCAS performs such correction.
No, the altitude on the transponder is corrected on the radar with the actual local QNH. It sends out in 1013 Hpa. Don’t mess with that.
Neil wrote:
things like static port positioning is so important
While I agree this is important, it’s unlikely the issue, I’d think that all the encoders in an SR22 are fed by the same static port lines, and what this here is is a discrepancy between the different altitude encoders / instruments.
To me it looks like Stephans plane is out of spec, Part 43 Appendix E (c) states that the altitude displayed in the altimeter is no more than 125ft different than the one reported by the Mode C transponder.
This requirement is very hard if you use different encoders for the altimeter and the transponder – the absolute error allowed exceeds this above FL200.
Peter wrote:
I use the up/down buttons on the KFC225 autopilot to adjust the actual altitude + / – 25ft until the FL readout on the transponder reads exactly right. Do you have such a FL display somewhere, Stephan?
Of course if the altitude encode is wrong then you are flying at precisely the wrong altitude.
Getting the transponder to tell ATC that you are at exactly their assigned level will keep them happy, but it doesn’t do anything for safety.
The fact that altimeters show differing readings demonstrates exactly why RVSM certification is not straightforward, and things like static port positioning is so important.
Hi Stephan, it seems that there’s a discrepancy between the pressure altitude indicated by your transponder and your altimeter?
What is your transponder showing when flying at FL200? Is it showing FL200 or FL202 ? On the function display of the GTX 330 you can switch to pressure alt:
When flying at the service ceiling with my aircraft (DA40) there is a 200ft difference between the primary (G1000) altimeter and the standby altimeter.
On the ground they indicate the same value. I always fly the altitude which is displayed on the G1000, as that is what is radiated by the transponder.
