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encoder approval

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Thu Aug 10, 2006 6:37 am Post subject: encoder approval

Responding to a posting from Skip Simpson:



8/10/2006



Hello Skip, The issue on the use of non TSO'd altitude encoders is currently 

under review (again) at FAA headquarters. I have been involved in this issue 

for some time, but have refrained from posting any information on this 

unresolved issue because of the potentially huge adverse impact upon our 

amateur built community. I wanted to avoid much controversial and 

distracting communications pending the, hopefully favorable, eventual ruling 

by FAA on this subject. Here in a fairly brief summary form is the 

situation:



1) FAR 91.217   Reads as follows: "Data correspondence between automatically 

reported pressure altitude data and the pilot's altitude reference.



No person may operate any automatic pressure altitude reporting equipment 

associated with a radar beacon transponder-



(a) When deactivation of that equipment is directed by ATC;



(b) Unless, as installed, that equipment was tested and calibrated to 

transmit altitude data corresponding within 125 feet (on a 95 percent 

probability basis) of the indicated or calibrated datum of the altimeter 

normally used to maintain flight altitude, with that altimeter referenced to 

29.92 inches of mercury for altitudes from sea level to the maximum 

operating altitude of the aircraft; or



(c) Unless the altimeters and digitizers in that equipment meet the 

standards of TSO-C10b and TSO-C88, respectively."



2) It would appear that any aircraft, standard type certificated or 

experimentally certificated, whether flying IFR or VFR, and replying with a 

mode C transponder altitude read out to ATC, either must comply with 91.217 

(b) or be using a TSO-C88 approved altitude encoder.



3) Some companies providing altitude encoders to the amateur built 

experimental aircraft community, some of which are incorporated into EFIS, 

have been providing non TSO'd altitude encoders. It is not always made clear 

by the manufacturing companies whether the altitude encoders within their 

EFIS are TSO'd or not.



4) Some of these non TSO'd altitude encoders have better performance than 

the TSO calls for both in terms of altitude granularity output and in output 

format (serial instead of gray code).



5) There are many of these non TSO'd encoders in aircraft that are currently 

flying and many in aircraft under construction.



6) A general presumption in the community was made (at least by those that 

thought about it) that if an altimeter - altitude encoder - transponder 

installation passed the FAR Part 43 Appendix E and F tests which are 

required by FAR 91.411 and 91.413 every two years, that FAR 91.217 (b) was 

being complied with.



7) A ruling from FAA headquarters in response to a letter from me said "not 

so" to such compliance interpretation in the following fashion:



"Your letter posed the following questions:



1.    If an amateur built experimental aircraft has an installed TSO'd ATC

transponder as required by Title 14 Code of Federal Regulations (14 CFR)

section 91.215, but a non-TSO'd altitude encoder and the installation has

passed the test and inspection requirements of 14 CFR sections 91.411 and

91.413 within the preceding 24 calendar months, does the installation meet

the requirements of 14 CFR section 91.217(b), and therefore make that

installation acceptable for IFR operations?



2.    If the answer to question one is No, can you please tell me

why?



The answer to question one is "No."  The testing required to show the

transmitted altitude data corresponds within 125 feet (on a 95 percent

probability basis) is more rigorous than the requirements referenced in 14

CFR sections 91.411, 91.413, and 14 CFR, part 43 appendices E and F.  The

tests required by 14 CFR part 43 appendix E(c) measure the automatic

pressure altitude at a sufficient number of test points to ensure the

altitude reporting equipment performs its intended function.

Title 14 CFR section 91.217 paragraphs (b) and (c), state that pressure

altitude reporting equipment must be tested and calibrated to transmit

altitude data correspondence within stated specifications; or, the

altimeters and digitizers must meet the standards in TSO-C10B and TSO-C88,

respectively.



Should the owner/operator elect to exhibit compliance with tests and

calibration provided in 14 CFR section 91.217(b), a test method would need 

to be developed that

ensures the transmitted data corresponds within 125 feet of the indicated

altitudes from sea level to the maximum operating altitude of the aircraft

on a 95 percent probability basis.  This testing also needs to ensure the

performance characteristics of the equipment are not impacted when

subjected to environmental conditions (voltage fluctuations temperature,

vibration, etc.) which may be encountered in airborne operations.

Completed tests and calibration results should be maintained in the

aircraft records.



Thank you for your interest in aviation safety."



 You can see the tremendous impact that enforcement of such a position 

would have on the companies making and selling non TSO'd encoders or EFIS 

containing non TSO'd encoders, the airplanes under construction planning to 

incorporate those EFIS, and all of those airplanes currently flying with non 

TSO'd altitude encoders.



9) I did not accept the FAA's position in 7) above as the final word and am 

working through a cooperating local FAA FSDO employee to both educate FAA 

headquarters and to get them to adopt a more reasonable position on the use 

of non TSO'd altitude encoders.



10) I would encouage our community to not react in an adverse manner to the 

FAA's current position and to continue to work the issue on a cooperative 

basis. I will post additional information as it becomes available and 

attempt to answer any questions that you may have.



OC -- The best investment we will ever make is in gathering knowledge.



<<Time: 09:12:25 PM PST US

From: CardinalNSB(at)aol.com

Subject: AeroElectric-List: Re: encoder approval



Is the Rocky Mountain encoder approved for certificated aircraft, the

factory says that "it conforms to c88a", is that enough, or is there more 

needed.



Any opinions on the unit.  Thanks, Skip  Simpson>>

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mike(at)ferrer-aviation.c
Guest

Posted: Tue Aug 15, 2006 7:39 am Post subject: encoder approval

 	  Quote: 	
		  From the EAA Website:


	


Q. Can a builder with a repairman certificate for the aircraft he built

perform his own altimeter or transponder certifications?



A. No. Although the FAR's do authorize the "manufacturer" of the aircraft to

conduct the tests, the builder of an amateur-built aircraft does not meet

the FAA's definition of a manufacturer. The FAA, in Order 8130.2, defines a

manufacturer as a Production Approval Holder (PAH). Some examples of a PAH

would be the holder of a Production Certificate (PC), a Parts Manufacturing

Authority (PMA), and Technical Standards Order Authorization (TSOA).

According to the FAA, an amateur builder does not fit this definition and,

therefore cannot perform the transponder and pitot/static tests on his/her

homebuilt.

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grosseair(at)comcast.net
Guest

Posted: Tue Aug 15, 2006 5:40 pm Post subject: encoder approval

Wow! You guys are getting way too intense about this whole thing! 

Lighten up and fly.



By now we should all realize that you can do any thing you want until it 

causes a problem. Then you'll find out that if you did the wrong thing 

you're violated, and your insurance may no longer cover you. But, hey, 

I've known of guys who flew for more than 20 years without a license or 

insurance. So just shut up and fly.



John Grosse

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