Avionics-List Digest Archive

Sat 08/12/06


Total Messages Posted: 3



Today's Message Index:
----------------------
 
     1. 02:29 PM - altitude encoders ()
     2. 03:29 PM - encoder approval ()
     3. 06:31 PM - encoder approval ()
 
 
 


Message 1


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    Time: 02:29:32 PM PST US
    From: <bakerocb@cox.net>
    Subject: altitude encoders
    --> Avionics-List message posted by: <bakerocb@cox.net> 8/12/2006 Responding to an AeroElectric-List message previously posted by Kevin Horton Hello Kevin, Thanks for your input. You wrote: "....skip......But, once Washington finds out the FSDO has approved something under 91.217(b) without requiring testing over the full range of conditions, they will probably release a policy letter that stops you in your tracks.....skip........" For the most part neither FAA headquarters nor FSDO's are aware of the situation. For years hundreds of non TSO'd altitude encoders with technology and performance superior to that called for in the TSO have been built, sold, installed, flying, tested satisfactorily every two years in accordance with FAR Part 43, and flying some more. I am not at risk of being stopped, I have a TSO'd altitude encoder in my flying amateur built experimental airplane, but I may want to build another plane with an EFIS and I want the EFIS developers and builders and the FAA to have reached a rational arrangement by that time. And I don't want that rational arrangement to include the FAA stifling the tremendous progress that has been made by EFIS developers by throwing a prohibitive bureaucratic blanket on the developers. Nor do I want all the airplanes presently flying with non TSO'd altitude encoders to be grounded. I think the solution lies in a more rational interpretation of the intent of FAR 91.217 (b). OC -- The best investment we will ever make is in gathering knowledge. <<AeroElectric-List message posted by: Kevin Horton <khorton01@rogers.com> Good luck. I think you are wasting your time, albeit for a good cause. Granted, you might manage to find some FSDO that doesn't understand that 95% probability does in fact mean over the full range of expected conditions (speaking from experience working with the aircraft cert FARs for many years). But, once Washington finds out the FSDO has approved something under 91.217(b) without requiring testing over the full range of conditions, they will probably release a policy letter that stops you in your tracks. I'm not saying that things should be like this, but this is the way they are, like it or not. The only way out, in my opinion, is a change to 91.217, but reg changes typically take 10 years or more. Kevin Horton>>


    Message 2


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    Time: 03:29:51 PM PST US
    From: <bakerocb@cox.net>
    Subject: encoder approval
    --> Avionics-List message posted by: <bakerocb@cox.net> 8/12/2006 Responding to an AeroElectric-List message previously posted by Kevin Horton Hello Again Kevin, Continuing our dialogue on our current favorite subject: 1) You wrote: "Do you agree that there are important safety-related reasons to require that the altitude encoder report the correct altitude, over the full range of conditions under which it will operate? Yes. 2) You wrote: " How can you be assured that a non-TSO'd encoder will operate correctly at temperature extremes, or when subjected to vibration, humidity, voltage variations, electromagnetic interference, etc? I would base my confidence in a proven non TSO'd altitude encoder on two things: A) The superior newer technology used in manufacturing the encoder. B) The actual past performance of that encoder over years of use in the field. 3) You wrote: "If the manufacturer hasn't tested his encoder under the full range of conditions, then he has no idea how well it will work there." I worked for years in the airborne weapons testing field and I assure you that there is no such thing as ground or laboratory testing "under the full range of conditions". Actual satisfactory performance in the field after a significant period time in use is the best indication of the suitability of a piece of equipment for its intended use. 4) You wrote: "If he has done the testing, and it does operate properly over the full range of conditions, why would the manufacturer not want to get a TSO for it? Two words -- time and money. When a small business sets out to create, manufacture, and sell a better mouse trap that it has developed it can only operate for so long on the capital available before some income has to arrive in order to sustain the business. If that capital is totally dissipated in un needed tests and bureaucratic paper generation before sufficient income arrives the company dies and the better mouse trap with it. 5) You wrote: "The fact that air traffic control has not detected a problem with someone's encoder says very little." You are right. But we are not talking about just someone's encoder. We are talking about hundreds of encoders that have been performing satisfactorily in flight for years and have satisfactorily passed the FAR Part 43 Appendices E and F tests many times every two years. 6) You wrote: "If there is a problem, it might not show up until another aircraft, responding to a TCAS alert tries to avoid your aircraft, yet hits it because the encode was in error. Is this acceptable?" No. But I say again, the technology used and the performance of the proven non TSO'd encoders is superior to that called for in the TSO. No piece of equipment can guarantee perfect peformance throughout its entire service life, but the better technology encoder is less likely to have a problem show up. 7) You wrote: "If you could write your own wording for 91.217, how would you word it to make it cheaper to comply, yet still achieve the safely objective?" My preferred first step in the process to resolve the present situation is an interpretation from FAA headquarters that automatic pressure altitude reporting equipment that is installed in amateur built experimental aircraft and tested in accordance with the appropriate provisions of FAR 91.411, 91.413, and appropriate Appendices to FAR Part 43 are considered to be in compliance with FAR 91.217 (b). I'll let the experts and lawyers work on a permanent rational solution. OC -- The best investment we will ever make is in gathering knowledge. <<AeroElectric-List message posted by: Kevin Horton <khorton01@rogers.com> Hi Owen, Do you agree that there are important safety-related reasons to require that the altitude encoder report the correct altitude, over the full range of conditions under which it will operate? How can you be assured that a non-TSO'd encoder will operate correctly at temperature extremes, or when subjected to vibration, humidity, voltage variations, electromagnetic interference, etc? If the manufacturer hasn't tested his encoder under the full range of conditions, then he has no idea how well it will work there. If he has done the testing, and it does operate properly over the full range of conditions, why would the manufacturer not want to get a TSO for it? The fact that air traffic control has not detected a problem with someone's encoder says very little. If there is a problem, it might not show up until another aircraft, responding to a TCAS alert tries to avoid your aircraft, yet hits it because the encode was in error. Is this acceptable? Note: recent regulatory changes will require more and more aircraft to get TCAS-like systems, so it will become even more important that all encoders be telling the truth. If you could write your own wording for 91.217, how would you word it to make it cheaper to comply, yet still achieve the safely objective? Kevin Horton>>


    Message 3


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    Time: 06:31:06 PM PST US
    From: <bakerocb@cox.net>
    Subject: encoder approval
    --> Avionics-List message posted by: <bakerocb@cox.net> 8/12/2006 Responding to an AeroElectric-List message previously posted by "Brian Meyette" Hello Brian, 1) You wrote: "What was the input you were responding to?' I assume that you were addressing this question to me. The input that I was responding to was a posting by Brett Ferrell. 2) You wrote: "What position is EAA referring to?" Brett included the EAA position on TSO'd encoders in his posting. He copied it off EAA's web site. I objected to the EAA position (as I described) and when they brushed me off I wrote to the FAA. I'll extract a bit of the EAA's position and copy it below: "The requirements for altitude reporting equipment associated with the transponder are called out in 91.217(c), which states that, the altimeters and digitizers must meet the standards of TSO-C10b and TSO-C88, respectively. TSO-C10b applies to the sensitive altimeter itself, and TSO-C88 applies to the automatic altitude reporting equipment. Again the equipment is required to meet the standards of the applicable TSO's, but not necessarily be produced under a TSO authorization. But as with the transponder, the easiest way for a builder to meet this requirement is to install equipment manufactured under a TSO authorization. Remember that, in order to legally operate this equipment under IFR, you must also comply with the maintenance and testing requirements of parts 91.411 (for altimeter and altitude reporting equipment), and 91.413 (for the transponder). Note that the requirements of 91.413 apply even if the aircraft is operated only under VFR." My objections were: A) The EAA position completely ignored the existence of FAR 91.217 (b). B) The EAA position completely ignored the existence of hundreds of amateur built experimental aircraft currently flying satisfactorily with non TSO'd transponders. C) The EAA position completely ignored the existence of EFIS incorporating non TSO'd transponders. D) I did not feel that the EAA position was proactive enough in support of their members interests. OC -- The best investment we will ever make is in gathering knowledge. PS: I greatly enjoyed looking at your web site. I shall return. <<AeroElectric-List message posted by: "Brian Meyette" <brianpublic2@starband.net> What was the input you were responding to? What position is EAA referring to? I went thru huge hassles over the encoder question. At that time, EAA was saying my encoder did not have to be TSOd. BMA & GRT said their built-in encoders were fine for IFR. But my avionics shop would not install or calibrate anything but TSOd. Local FSDO agreed. I hassled over it for months & ended up buying the Sandia TSO encoder. Details beginning here: http://brian76.mystarband.net/avionicsAug04.htm#aug31>>




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