Avionics-List Digest Archive

Sat 03/27/10


Total Messages Posted: 1



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     1. 12:50 PM - Update on non TSO'd altitude encoders ()
 
 
 


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    Time: 12:50:00 PM PST US
    From: <bakerocb@cox.net>
    Subject: Update on non TSO'd altitude encoders
    3/27/2010 Mr. Baker, I do not have any new info on this subject. The FAA has not issued any statement regarding TSO equipment or installation either specifically for encoders or for any other equipment on the aircraft. The question has been asked many times to many FAA offices. Their response to date has been the same - no response at all beyond "we'll get back to you". I assure you that if we ever do get a response in writing that we can publish, we will do so at once. It's a question that needs answering, and we will continue to pursue an answer. Unfortunately, to date we have not had any success in this endeavor. Stay tuned! When we know something we'll get the word out pronto. Joe Norris EAA 113615 Lifetime Homebuilders Community Manager EAA-The Spirit of Aviation Phone: 888.322.4636 Extension 6806 Fax: 920.426.4873 =========================================================== 2/18/2010 Hello Mr. Norris, From time to time the subject of using a non TSO'd altitude encoder in amateur built experimental aircraft comes up on the Matronics aeroelectric list. Copied below is one of those postings. No favorable response on this subject has ever been received from FAA Headquarters. Many more postings on this subject can be found by searching for "non TSO'd altitude encoders" at this web site: http://www.matronics.com/searching/ws_script.cgi The last thing that I read from EAA to resolve this situation was a suggestion that the builder just purchase and install a TSO'd altitude encoder (in addition to the non TSO'd altitude encoder incorporated into the EFIS) in order to meet the FAA requirements. Do you have any additional information to add on this subject at this time? Thank you, Owen C. Baker EAA 0073580 ============================================================= #32094 From: <bakerocb(at)cox.net> 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." 8) 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. =================================================== 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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