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Flying to close, what would you have done, if anything.


Danb

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Interesting.  I guess I never thought much about it butI think you may be overthinking this whole thing.

 With a blind encoder it transmits pressure altitude which is interpreted by ATC radar using local baro pressure.  It doesn't matter what you have in the window.

An encoding altimeter transmits the altitude that is in the coleman window.  I used to have one till it went TU.

That leaves the last question.  ADS-b and traffic presentation.  Although I am not fully versed on on the inner workings of ADS-b, it would make sense that the presentation in the cockpit would be based on ADS-b data (baro pressure) and blind encoding of the other aircraft.  Since ADS-b out actively interrogates other aircraft, there must be a way for it to discern MSL altitude of the other aircraft and present to you an above/below altitude solution.  

All the targets I have seen through TIS-b have been right on.  IT will be interesting to see if that changes with the installation of the Stratus ESG that is being installed as I write this.

I don't know all the in's and out's of TCAS, but I imagine it works much the same way.  IT will present targets regardless of who they are talking to.  The only difference between TCAS and ADS-b traffic is, TCAS gives you resolution alerts.

 

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I did not realize that an encoding altimeter transmits the altitude based on your Kollsman window setting. That seems like it would give serious grief to ATC; how would they know whether or not to adjust your displayed altitude for local pressure?


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With an encoder, it's important that the correct altimeter setting is in the window.

When mine went, the altimeter itself broke and wound all the way to FL280. ATC asked me to verify my altitude and that he showed me in the flight levels.
I told him, although a Mooney has pretty good performance, I was pretty sure I was not in the flight levels presently. :). He agreed. I made a $1800 stop and, voila.. new altimeter!

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Stand by...

I am going to look up some details.

The IR training has a lot of details that are a challenge to remember.

Hank and I have/had barometers where the kollsman's window was not attached to the encoder.  See the definitions of blind encoder and matched components in the next post of mine.

Some reading in the mean time...

https://en.m.wikipedia.org/wiki/Paul_Kollsman

Kollsman was a tech guru and commercial superstar!

 

I came across some FAA details that includes definitions...

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC 43-6C.pdf

 

Best regards,

-a-

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The definition of an encoding altimeter describe pressure altitude being used...  see where I underlined #6....

And of course pressure altitude is...

In aviationpressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting under certain circumstances where the aircraft's altimeter would be unable to give a useful readout of altitude. Examples would be landing at a very high altitude or near sea level in conditions of exceptionally high air pressure. Old altimeters were typically limited to show altitude when set between 950 mbar and 1030 mbar. "Standard" pressure, the baseline used universally, is 1013.25 hPa, equivalent to 1013.25 mbar or 29.92 inHg (inches of mercury). This setting is equivalent to the air pressure at mean sea level (MSL) in the International Standard Atmosphere (ISA). Pressure altitude is primarily used in aircraft performance calculations and in high-altitude flight (above the transition altitude).

-------------------------------------------------------

9/17/12

APPENDIX 2. DEFINITIONS
1. Approved.
Unless used with reference to another person, means approved by the

Administrator.

AC 43-6C Appendix 2

2. Blind Encoder (Digitizer). An altitude reporting encoder that is pressure operated, having no altitude display; is not part of a pressure/altitude indicating device or system; does not contain an external means for barometric setting; and may supply altitude reporting information to the air traffic control (ATC) transponder, Global Positioning System (GPS), or other onboard system.

3. Calibrated Datum of the Altimeter. The correction applied via a specific calibration card applicable to a specific altimeter to correct for instrument error (scale error) only.

4. Correspondence. The maximum absolute difference between altimeter display and encoder output for a constant encoder output. The altimeter’s displayed pressure/altitude
(referenced to 29.92) compared to encoded altitude output from the blind encoder or encoding altimeter for the entire period (from the moment that the code output changes to a value to the moment the code output changes to the next value while the pressure/altitude is changing).

5. Data. Drawings, sketches, stress analyses, reports, operating limitations, or photographs that support or describe an alteration.

6. Encoding Altimeter (Pressure Altitude). An altitude indicator that displays to the pilot the pressure/altitude sensed by the device and produces an altitude reporting output.

7. Gillham Encoder. An altitude reporting encoder that provides parallel data output employing the Gillham (Grey) code.

8. Indicated Datum of the Altimeter. The altitude displayed by the altimeter when an ideal absolute pressure is applied to the sensing member of the altimeter and not corrected for instrument error (scale error), nor corrected for static source error.

9. Matched Components. An altimeter and a blind encoder that have been tested and calibrated together and, as a combination, meet the requirements of 14 CFR part 91, § 91.411(a).

10. High Reliability Style Connectors. Connectors designed to or meeting Military or similar industry standards.

11. Pilot Reference Altimeter. The altimeter normally used to maintain flight altitude. 

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