S

sblack

Well Known Member
Can you US folks explain the requirements for altimeter and transponder/encoder qualification when using a non certified EFIS as the primary source for altitude information? Our regulators here in Canada are throwing some curve balls at us that don't make sense so I would like to know what your requirements are. Any help greatly appreciated.
 
In the US, the altimeter, whether it is a certified EFIS or not, still has to pass the requirements of FAR 43 Appendix E. In the experimental world, most of the EFIS are not certified but can be used as primary altitude reporting. In Canada, if I remember correct, they require a certified altimeter in addition to your EFIS for IFR flight. I do not know of any non-certified transponders, but I can see them having an issue using an EFIS (non certified source) to provide encoded altitude to the transponder which will force you to use the old blind encoder.
 
For VFR flight: (Ref CFR 91.413/43 (f)
1) There are no altimeter checks or accuracy requirements.
2) Primary Altimeter and altitude encoder must match within 125 ft of each other (data correspondence).
3) Transponder must be tested every 2 years.

For IFR: (ref CFR 91.411/43 (e) and 91.413/43 (f)
1) Altimeter/EFIS must pass a number of tests including accuracy.
2) Altitude encoder must match primary altimeter within 125 ft.
3) Static system must pass leak test.
4) Transponder must pass funtional tests.

For experimentals TSO's are not required for altimetry items but they must pass all the required tests.
 
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Canada vs USA

The OP is posting from Canada.

Walt is quoting USA regulations.

"Never the twain shall meet." (I just made that up. :rolleyes:)

Not all rules/regs are the same.

FWIW
 
PCHunt said:
The OP is posting from Canada.
Walt is quoting USA regulations.
"Never the twain shall meet." (I just made that up. :rolleyes:)
Not all rules/regs are the same.
FWIW
Click to expand...

But he's asking about US rules!
 
Thanks for the replies. How well do the EFIS altimeters usually check out?

The hysteresis check seems redundant for an electronic sensor. I figured that was more for a mechanical gauge where there are gears that wear, backlash etc I would not expect an electronic sensor to have any of that.
 
sblack said:
Thanks for the replies. How well do the EFIS altimeters usually check out?
The hysteresis check seems redundant for an electronic sensor. I figured that was more for a mechanical gauge where there are gears that wear, backlash etc I would not expect an electronic sensor to have any of that.
Click to expand...

My transponder guy claims that he's never had a problem with any of the EFISs.
 
sblack said:
Thanks for the replies. How well do the EFIS altimeters usually check out?

The hysteresis check seems redundant for an electronic sensor. I figured that was more for a mechanical gauge where there are gears that wear, backlash etc I would not expect an electronic sensor to have any of that.
Click to expand...

Overall I have found EFIS systems to have excellent accuracy and generally better than their aneroid counter parts (aneroid altimeters can be amazingly accurate and are extremely reliable).

EFIS systems are still subject to errors and sensor drift so recalibration is required occasionally even on the best ones.

Even though friction and hysteresis are not really applicable they are still required tests per the regs.

I am still waiting on a replacement sensor module for a brand new experimental EFIS I installed where the altitude and airspeed was way out of limits straight out of the box (I'm not sure how something like this gets out of the "factory") and I've seen failed ADAHRS units that were 500ft off, so they may be great gee whiz stuff but they are not perfect.

Bottom line, I've probably seen more failed (out of limits) experimental EFIS units than their mechanical aneroid counter-parts. The failure mechanisms are different, mechanical altimeters usually fail due to case leaks or excessive friction (just getting old) while an EFIS unit will fail and go out of limits.

And just some thoughts; systems used to have an altimeter and an altitude encoder which are 2 sources of altitude, so if ATC questions your altitude it can alert you to an altitude discrepancy with one of your units. With todays EFIS system our EFIS unit is reporting the same altitude (ref to 29.92) that we see on our screen to ATC, so if your EFIS is off ATC won't know, so you may be 500 ft off altitude and you would never know as ATC will see your incorrect altitude as well; so we've lost a level of redundancy here. Hence I would recommend having 2 sources of altimetry with an EFIS (dual ADAHRS) or EFIS and aneroid.
 
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