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CardinalNSB(at)aol.com
Guest

Posted: Wed Aug 09, 2006 8:12 pm Post subject: encoder approval

Is the Rocky Mountain encoder approved for certificated aircraft, the0 factory says that "it conforms to c88a", is that enough, or is there more0 needed.

  

 Any opinions on the unit.  Thanks, Skip0 Simpson

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>>

bferrell(at)123mail.net
Guest

Posted: Thu Aug 10, 2006 8:13 am Post subject: encoder approval

Have you enlisted the help of EAA on this matter?  I would think that thier

involvement would be helpful.  They've already weighed in on this matter, in

the other direction, supposedly with FAA input!!



http://members.eaa.org/home/homebuilders/faq/1Equipping%20a%20Homebuilt%20for%20IFR%20operations.html?

(or tiny)

http://tinyurl.com/s5uzc



which says

"What about TSO’s?



Another question to be answered is what, if any, of the equipment needs to be

“TSO’ed”. In order to address this question, it’s helpful to understand what a

“TSO” is. TSO stands for Technical Standard Order, which is defined in 14 CFR

Part 21, section 21.601(b)(1) as “….a minimum performance standard for

specified articles (for the purpose of this subpart, articles means materials,

parts, processes, or appliances) used on civil aircraft.” As you can see from

this definition, a TSO is actually a performance standard to which an article

can be manufactured.



When someone says an article is “TSO’ed”, what they really mean is that the unit

was manufactured under a TSO authorization. Section 21.601(b)(2) says, “A TSO

authorization is an FAA design and production approval issued to the

manufacturer of an article which has been found to meet a specific TSO”. You’ll

note that the TSO and TSO authorization deal specifically with design and

manufacture, and have nothing to do with installation or operation.



Now we have an idea what a TSO is, but we still haven’t answered the question of

whether or not our instruments and avionics in a homebuilt need to be “TSO’ed”.

Our Operating Limitations state that we have to equip the aircraft in

accordance with 91.205, and 91.205 lists the minimum equipment required, but

nowhere is there mention of a requirement for TSO’ed equipment. Thus, the

answer is NO, the instruments and equipment installed in your homebuilt under

the requirements of 91.205 are not required to be “TSO’ed”.



So far, so good, but that’s not the whole story. Most builders who plan to equip

their homebuilt for IFR operations don’t stop at the minimums, so let’s take a

look at some of the other commonly installed equipment and see what’s required.



Transponders and related equipment;



One item that will be high on the list of desired equipment will be a

transponder. It’s interesting to note that 91.205 does not list a transponder

as required in order to operate under IFR. While this is true, our current

airspace system as well as the advantages for use in both IFR and VFR

operations makes a transponder a popular choice for builders when outfitting

their aircraft.



The requirements for transponder equipment and operation are found in 91.215,

which has this to say:



(a) All airspace: U.S.-registered civil aircraft. For operations not conducted

under part 121 or 135 of this chapter, ATC transponder equipment installed must

meet the performance and environmental requirements of any class of TSO-C74b

(Mode A) or any class of TSO-C74c (Mode A with altitude reporting capability)

as appropriate, or the appropriate class of TSO-C112 (Mode S).



Note that, while it is required that the transponder equipment meet the

performance and environmental requirements of the applicable TSO, it is not

required that the equipment be manufactured under a TSO authorization. In

theory, this means that you could actually build your own transponder, so long

as you can document that it meets the requirements of the applicable TSO.

However, the easiest way to be assured that your transponder meets the

requirements of 91.215(a) is to install one that has been built under a TSO

authorization.



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."



Brett



Quoting bakerocb(at)cox.net:



 	  Quote: 	
		   



 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

 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: 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>>

khorton01(at)rogers.com
Guest

Posted: Thu Aug 10, 2006 5:25 pm Post subject: encoder approval

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



On 10 Aug 2006, at 10:36, <bakerocb(at)cox.net> <bakerocb(at)cox.net> wrote:



 	  Quote: 	
		   



 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.

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 4:28 am Post subject: encoder approval

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



On 11 Aug 2006, at 07:23, <bakerocb(at)cox.net> wrote:



 	  Quote: 	
		   



 8/11/2006



 Responding to an AeroElectric-List message previously posted by  

 Kevin Horton.



 Hello Kevin, Time spent in attempting to correct an injustice or an  

 absurdity by governments is never wasted. It  is a peculiarity of  

 human nature that once people are placed in a position of authority  

 or officialdom that a percentage of them will abuse that position  

 either out of ignorance or arrogance. Left unchallenged, that abuse  

 never diminishes on its own, but instead tends to grow.



 The current situation is that every day companies are manufacturing  

 and selling more non TSO'd encoders that are better than the TSO  

 calls for, some builder are buying those encoders or have bought  

 them in the past, avionics shops are approving those non TSO'd  

 encoders in accordance with the tests called for in FAR Part 43  

 Appendix E and F, and many airplanes (hundreds? thousands?)  are  

 flying around with those encoders responding with an altitude  

 readout that ATC is entirely satisfied with.



 And FAA headquarters currently says: "No, that can't be because it  

 is in violation of FAR 91.217 (b) as we interpret it."



 I don't know how this situation would eventually resolve itself if  

 we just ignored it, but I don't feel that a head-in-the-sand  

 approach is the best way to go.



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



 <<AeroElectric-List message posted by: Kevin Horton  

 <khorton01(at)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>>






	


Kevin Horton

Ottawa, Canada

brianpublic2(at)starband.
Guest

Posted: Fri Aug 11, 2006 7:02 am Post subject: encoder approval

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

--

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Aug 11, 2006 8:47 am Post subject: encoder approval

On Aug 11, 2006, at 8:08 AM, Kevin Horton wrote:



 	  Quote: 	
		   

 <khorton01(at)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 do you know that a TSO'd encoder will do the same? Many encoders  

fail, even those meeting TSO at teh time of manufacture. The best  

cross check is to have a transponder that reports pressure altitude  

from the encoder (my SL-70 does) and cross-reference that to the  

mechanical altimeter. Also, if you are on flight following with ATC  

and deviate from your altitude by more than 300', even if you are  

VFR, the will most likely ask you to check your altimeter setting. At  

that point you know that something is amiss if your mechanical  

altimeter says you are on your chosen altitude.



So I don't see TSO or type acceptance as being all that valuable.  

Cross checking the instruments strikes me as far more interesting.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 9:31 am Post subject: encoder approval

On 11 Aug 2006, at 12:45, Brian Lloyd wrote:

 	  Quote: 	

 yak(at)lloyd.com>

 On Aug 11, 2006, at 8:08 AM, Kevin Horton wrote:

> 

> <khorton01(at)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 do you know that a TSO'd encoder will do the same? Many  

 encoders fail, even those meeting TSO at teh time of manufacture.  

 The best cross check is to have a transponder that reports pressure  

 altitude from the encoder (my SL-70 does) and cross-reference that  

 to the mechanical altimeter. Also, if you are on flight following  

 with ATC and deviate from your altitude by more than 300', even if  

 you are VFR, the will most likely ask you to check your altimeter  

 setting. At that point you know that something is amiss if your  

 mechanical altimeter says you are on your chosen altitude.

 So I don't see TSO or type acceptance as being all that valuable.  

 Cross checking the instruments strikes me as far more interesting.

Interesting point.  I agree that regular monitoring of the encoder  

output and/or flight following might address the issue.  But I  

suspect that many pilots wouldn't regularly monitor the encoder  

output, and a lot of folks don't like flight following.  Can't have  

the UN know what you are doing all the time you know 

Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Aug 11, 2006 10:20 am Post subject: encoder approval

On Aug 11, 2006, at 1:28 PM, Kevin Horton wrote:

 	  Quote: 	
		  > So I don't see TSO or type acceptance as being all that valuable.  

> Cross checking the instruments strikes me as far more interesting.

 Interesting point.  I agree that regular monitoring of the encoder  

 output and/or flight following might address the issue.  But I  

 suspect that many pilots wouldn't regularly monitor the encoder  

 output, and a lot of folks don't like flight following.  Can't have  

 the UN know what you are doing all the time you know 

Given the proliferation of TFRs with fires and the mindless  

wanderings of politicians during mating season with the electorate  

down here, (ah, I feel another screwing coming on) it is almost  

necessary to use ATC advisories in the US now. Gone is the time when  

I used to fly without advisories while listening to my iPod and  

enjoying the scenery.

(There is only one area in my common comings and goings where I don't  

feel I have to deal with ATC and that is just after leaving Haitian  

airspace and before reaching the airspace around Nassau. The Bahamian  

waters are beautiful blue-green; the airplanes nonexistant; and the  

airspace non-US. The only down side is that there is no one to talk  

to should I encounter a problem.)

Given that more people are going for all-in-one PFDs like Dynon, et  

al, one is going to want to have a cross-reference for altitude. This  

means a display for your encoder. By having a second air-data device  

with a display you can cross check with your PFD. Something to think  

about.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

chaztuna(at)adelphia.net
Guest

Posted: Fri Aug 11, 2006 10:33 am Post subject: encoder approval

At 01:28 PM 8/11/2006, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Kevin Horton <khorton01(at)rogers.com>



 On 11 Aug 2006, at 12:45, Brian Lloyd wrote:



  	  Quote: 	
		  --> AeroElectric-List message posted by: Brian Lloyd <brian- yak(at)lloyd.com>



 

 On Aug 11, 2006, at 8:08 AM, Kevin Horton wrote:



  	  Quote: 	
		  --> AeroElectric-List message posted by: Kevin Horton  

 <khorton01(at)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 do you know that a TSO'd encoder will do the same? Many  

 encoders fail, even those meeting TSO at teh time of manufacture.  

 The best cross check is to have a transponder that reports pressure  

 altitude from the encoder (my SL-70 does) and cross-reference that  

 to the mechanical altimeter. Also, if you are on flight following  

 with ATC and deviate from your altitude by more than 300', even if  

 you are VFR, the will most likely ask you to check your altimeter  

 setting. At that point you know that something is amiss if your  

 mechanical altimeter says you are on your chosen altitude.



 So I don't see TSO or type acceptance as being all that valuable.  

 Cross checking the instruments strikes me as far more interesting. 	


 Interesting point.  I agree that regular monitoring of the encoder  

 output and/or flight following might address the issue.  But I  

 suspect that many pilots wouldn't regularly monitor the encoder  

 output, and a lot of folks don't like flight following.  Can't have  

 the UN know what you are doing all the time you know 



 Kevin Horton         RV-8 (finishing kit)

 Ottawa, Canada

  http://www.kilohotel.com/rv8 	


 Kevin,

  One of the really neat features of the RMI uEncoder is that it's OAT sensor and internal circuitry allow it to display not only indicated altitude, but also density altitude,pressure altitude, true altitude AND reported (encoder) altitude. See the link below to go to the uEncoder features link once on the main page for more info.



  http://www.rkymtn.com/



 With a separate altimeter to check against, it's very easy to determine if the encoder develops an error. I suspect that most of the EFISs also have this feature.

 Charlie Kuss

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 11:26 am Post subject: encoder approval

On 11 Aug 2006, at 14:16, Brian Lloyd wrote:



 	  Quote: 	
		   

 yak(at)lloyd.com>



 On Aug 11, 2006, at 1:28 PM, Kevin Horton wrote:



>> So I don't see TSO or type acceptance as being all that valuable.  

>> Cross checking the instruments strikes me as far more interesting.

>

> Interesting point.  I agree that regular monitoring of the encoder  

> output and/or flight following might address the issue.  But I  

> suspect that many pilots wouldn't regularly monitor the encoder  

> output, and a lot of folks don't like flight following.  Can't  

> have the UN know what you are doing all the time you know 



 Given that more people are going for all-in-one PFDs like Dynon, et  

 al, one is going to want to have a cross-reference for altitude.  

 This means a display for your encoder. By having a second air-data  

 device with a display you can cross check with your PFD. Something  

 to think about.




	


The Dynon EFIS is capable of acting as an encoder, and I would bet  

you a case of beer that there are aircraft flying with the Dynon EFIS  

acting as an encoder, with no other altimeter on the aircraft.  Now  

there is absolutely nothing to cross check against.  Now even flight  

following won't help, as the pilot would be trying to fly to the same  

possibly erroneous altitude source that ATC would be looking at.



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Aug 11, 2006 12:00 pm Post subject: encoder approval

On Aug 11, 2006, at 3:24 PM, Kevin Horton wrote:



 	  Quote: 	
		   The Dynon EFIS is capable of acting as an encoder, and I would bet  

 you a case of beer that there are aircraft flying with the Dynon  

 EFIS acting as an encoder, with no other altimeter on the  

 aircraft.  Now there is absolutely nothing to cross check against.   

 Now even flight following won't help, as the pilot would be trying  

 to fly to the same possibly erroneous altitude source that ATC  

 would be looking at.


	


Bingo. I rather like the Rocky Mountain microencoder.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

mprather(at)spro.net
Guest

Posted: Fri Aug 11, 2006 12:18 pm Post subject: encoder approval

I'll chime in here too...



I also like WAAS enhanced GPS altitude.  My little Garmin backpacker

handheld displays it, and it has only once been off more than 100ft or

so..  And that was when the altimeter in the airplane I was flying got

seriously stuck...  I was climbing to get over some terrain that I am

fairly familiar with, and realized that the sight picture didn't make

sense compared to what I was used to seeing (at the altitude I thought I

was climbing through).  I was trying to resolve that when I happened to

glance at the GPS which I often wedge between the glareshield and the

windshield and noticed that there was almost exactly 2000ft of discrepancy

between the GPS altitude and the baro instrument (I was at that time at

about 10.5k' MSL, not the planned 8.5kMSL).  ???  So, I touched the adjust

knob on the baro instrument, and almost instantly the hands wound around

to match up with the GPS reading.  ???  Gives you a very funny feeling.  I

am certainly glad nothing like that has happened IFR.



The above said, a baro encoder with an extra display is a nice thing.  The

T2000 txp in my Varieze displays encoder altitude, and has an adjustment

which allows correction for barometric pressure.  While certainly not as

slick as the micro encoder, it does the job.

Regards,



Matt-



 	  Quote: 	
		   At 01:28 PM 8/11/2006, you wrote:

>

> <khorton01(at)rogers.com>

>

>On 11 Aug 2006, at 12:45, Brian Lloyd wrote:

>

>>

>> yak(at)lloyd.com>

>>

>>

>>On Aug 11, 2006, at 8:08 AM, Kevin Horton wrote:

>>

>>>

>>><khorton01(at)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 do you know that a TSO'd encoder will do the same? Many

>>encoders fail, even those meeting TSO at teh time of manufacture.

>>The best cross check is to have a transponder that reports pressure

>>altitude from the encoder (my SL-70 does) and cross-reference that

>>to the mechanical altimeter. Also, if you are on flight following

>>with ATC and deviate from your altitude by more than 300', even if

>>you are VFR, the will most likely ask you to check your altimeter

>>setting. At that point you know that something is amiss if your

>>mechanical altimeter says you are on your chosen altitude.

>>

>>So I don't see TSO or type acceptance as being all that valuable.

>>Cross checking the instruments strikes me as far more interesting.

>

>Interesting point.  I agree that regular monitoring of the encoder

>output and/or flight following might address the issue.  But I

>suspect that many pilots wouldn't regularly monitor the encoder

>output, and a lot of folks don't like flight following.  Can't have

>the UN know what you are doing all the time you know 

>

>Kevin Horton         RV-8 (finishing kit)

>Ottawa, Canada

>http://www.kilohotel.com/rv8



 Kevin,

   One of the really neat features of the RMI uEncoder is that it's

 OAT sensor and internal circuitry allow it to display not only

 indicated altitude, but also density altitude,pressure altitude, true

 altitude AND reported (encoder) altitude. See the link below to go to

 the uEncoder features link once on the main page for more info.



 http://www.rkymtn.com/



 With a separate altimeter to check against, it's very easy to

 determine if the encoder develops an error. I suspect that most of

 the EFISs also have this feature.

 Charlie Kuss

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 1:20 pm Post subject: encoder approval

Yes, WAAS enhanced GPS altitude can save you from large errors, as  

happened to you.  But, everyone needs to understand that barometric  

altitude, as seen on an altimeter is not at all the same thing as GPS  

altitude.  They can be differ by many hundreds of feet if the  

temperature is significantly different from standard.  In cold  

temperatures the altimeter will read high than the GPS, and in warm  

temperatures it will read lower.  The difference will be about 4% for  

every 10 deg C that the temperature differs from standard.  The  

difference will be zero on the ground at the airport where the  

altimeter setting came from, and will count up from there.  E.g, if  

you were at 5500 ft, with an altimeter setting that came from an  

airport at 500 ft, and the temperature was 25 deg C colder than  

standard, the altimeter would read about 500 ft higher than the GPS.



The air traffic system is built on the premise that people will fly  

specific barometric altitudes (i.e. based on a barometric  

altimeter).  If you use GPS altitude, you may be negating the  

altitude separation that is assumed.  In the example above, a guy  

flying VFR who wanted to be at 5500 ft, and decided to use his GPS as  

the altitude reference, would actually be at about 6000 ft barometric  

altitude, right at an IFR altitude.  Not good.



If you see a significant difference between your altimeter and your  

GPS, please continue to fly the altimeter, unless you are in cloud,  

at an altitude where obstacle clearance is a concern.  In this case,  

declare an emergency, tell ATC you really don't know what your  

altitude is, and use which ever one is indicating lower as your  

reference.  Get your altimeter checked by an avionics shop before the  

next flight.



Kevin Horton



On 11 Aug 2006, at 16:16, Matt Prather wrote:



 	  Quote: 	
		   

 <mprather(at)spro.net>



 I'll chime in here too...



 I also like WAAS enhanced GPS altitude.  My little Garmin backpacker

 handheld displays it, and it has only once been off more than 100ft or

 so..  And that was when the altimeter in the airplane I was flying got

 seriously stuck...  I was climbing to get over some terrain that I am

 fairly familiar with, and realized that the sight picture didn't make

 sense compared to what I was used to seeing (at the altitude I  

 thought I

 was climbing through).  I was trying to resolve that when I  

 happened to

 glance at the GPS which I often wedge between the glareshield and the

 windshield and noticed that there was almost exactly 2000ft of  

 discrepancy

 between the GPS altitude and the baro instrument (I was at that  

 time at

 about 10.5k' MSL, not the planned 8.5kMSL).  ???  So, I touched the  

 adjust

 knob on the baro instrument, and almost instantly the hands wound  

 around

 to match up with the GPS reading.  ???  Gives you a very funny  

 feeling.  I

 am certainly glad nothing like that has happened IFR.



 The above said, a baro encoder with an extra display is a nice  

 thing.  The

 T2000 txp in my Varieze displays encoder altitude, and has an  

 adjustment

 which allows correction for barometric pressure.  While certainly  

 not as

 slick as the micro encoder, it does the job.

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Aug 11, 2006 2:14 pm Post subject: encoder approval

On Aug 11, 2006, at 5:17 PM, Kevin Horton wrote:



 	  Quote: 	
		   

 <khorton01(at)rogers.com>



 Yes, WAAS enhanced GPS altitude can save you from large errors, as  

 happened to you.  But, everyone needs to understand that barometric  

 altitude, as seen on an altimeter is not at all the same thing as  

 GPS altitude.  They can be differ by many hundreds of feet if the  

 temperature is significantly different from standard.


	


When flying at 14,000' or so in the dead of winter I have seen errors  

as much as 2000'. (This is another reason MEAs have lots of margin  

built into them.)

 	  Quote: 	
		  

 The air traffic system is built on the premise that people will fly  

 specific barometric altitudes (i.e. based on a barometric  

 altimeter).  If you use GPS altitude, you may be negating the  

 altitude separation that is assumed.  In the example above, a guy  

 flying VFR who wanted to be at 5500 ft, and decided to use his GPS  

 as the altitude reference, would actually be at about 6000 ft  

 barometric altitude, right at an IFR altitude.  Not good.


	


This is what the altitude correction section on your E6B is for. Play  

with it. Plug in temp and pressure altitude and see what the  

correction factor is. If you correct the barometric altimeter for  

pressure and temperature you will find it will compare favorably with  

what your GPS reads out.



 	  Quote: 	
		   If you see a significant difference between your altimeter and your  

 GPS, please continue to fly the altimeter, unless you are in cloud,  

 at an altitude where obstacle clearance is a concern.  In this  

 case, declare an emergency, tell ATC you really don't know what  

 your altitude is, and use which ever one is indicating lower as  

 your reference.  Get your altimeter checked by an avionics shop  

 before the next flight.


	


Good advice but try your E6B first. Most of us never spend any time  

with this feature when learning to fly but it can make a big  

difference when you are in a marginal climb condition and wondering  

if you are going to be 100' above or 100' below the ridgeline you are  

thinking of crossing. Believe me, 100' can make a big difference  

between having a good hair day and a bad hair day.



I have been flying for a lot of years (38 now) and, believe it or  

not, I still use my E6B on almost *every* flight (even if for nothing  

more than TAS conversion). It is still the same old aluminum  

Sanderson E6B my father gave me when I was 15 and getting ready to  

take ground school. It still works and the batteries still haven't  

worn out.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 3:00 pm Post subject: encoder approval

On 11 Aug 2006, at 18:10, Brian Lloyd wrote:

 	  Quote: 	

 yak(at)lloyd.com>

 On Aug 11, 2006, at 5:17 PM, Kevin Horton wrote:

> 

> <khorton01(at)rogers.com>

>

> Yes, WAAS enhanced GPS altitude can save you from large errors, as  

> happened to you.  But, everyone needs to understand that  

> barometric altitude, as seen on an altimeter is not at all the  

> same thing as GPS altitude.  They can be differ by many hundreds  

> of feet if the temperature is significantly different from standard.

 Good advice but try your E6B first. Most of us never spend any time  

 with this feature when learning to fly but it can make a big  

 difference when you are in a marginal climb condition and wondering  

 if you are going to be 100' above or 100' below the ridgeline you  

 are thinking of crossing. Believe me, 100' can make a big  

 difference between having a good hair day and a bad hair day.

To be honest, I had completely forgotten that an E6B had this  

feature.  Now I have to try to find mine 

I wouldn't really on any calculation if you only have a few hundred  

feet of obstacle clearance, if you are at altitude.  The calculation  

is only accurate if you can account for the temperature difference  

from ISA at every point from the airport to altitude.  The rule of  

thumb (and the E6B) use a single number for the temperature  

difference, rather than try to use the varying temperature errors at  

various altitudes.  That is a bit of a long way to say that the  

correction factors are only approximate in any real world case.  If  

you calculate 100 ft of obstacle clearance, turn back, please.  I'd  

want to calculate at least 1000 ft of clearance, ideally even more.

Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Aug 11, 2006 3:47 pm Post subject: encoder approval

On Aug 11, 2006, at 6:57 PM, Kevin Horton wrote:



 	  Quote: 	
		   To be honest, I had completely forgotten that an E6B had this  

 feature.  Now I have to try to find mine 


	


I was completely blown away at the cool stuff I could do with my E6B  

back when I was a kid. I still am.

 	  Quote: 	
		  

 I wouldn't really on any calculation if you only have a few hundred  

 feet of obstacle clearance, if you are at altitude.  The  

 calculation is only accurate if you can account for the temperature  

 difference from ISA at every point from the airport to altitude.   

 The rule of thumb (and the E6B) use a single number for the  

 temperature difference, rather than try to use the varying  

 temperature errors at various altitudes.  That is a bit of a long  

 way to say that the correction factors are only approximate in any  

 real world case.  If you calculate 100 ft of obstacle clearance,  

 turn back, please.  I'd want to calculate at least 1000 ft of  

 clearance, ideally even more.


	


<sigh> Some people just get too literal.  The point I think we  

both were making was that the altimeter lies. It always lies except  

when you are on the ground and you turn the kollsman knob to make it  

read airport elevation. (Have you ever noticed that sometimes when  

you do that it doesn't match the altimeter setting from the nearby  

airport with an ATIS that happens to be at a different altitude?)



But all kidding aside, there really are significant errors and they  

get worse as you go up and the temp differs from ISA. But you do only  

need OAT and p-alt to get the correction factor. Does the Rocky  

Mountain uEncoder provide true altitude? Ah, I see that it does.  

Seems like a good thing.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

khorton01(at)rogers.com
Guest

Posted: Fri Aug 11, 2006 5:04 pm Post subject: encoder approval

On 11 Aug 2006, at 19:44, Brian Lloyd wrote:



 	  Quote: 	
		   

 yak(at)lloyd.com>



 On Aug 11, 2006, at 6:57 PM, Kevin Horton wrote:

>

> I wouldn't really on any calculation if you only have a few  

> hundred feet of obstacle clearance, if you are at altitude.  The  

> calculation is only accurate if you can account for the  

> temperature difference from ISA at every point from the airport to  

> altitude.  The rule of thumb (and the E6B) use a single number for  

> the temperature difference, rather than try to use the varying  

> temperature errors at various altitudes.  That is a bit of a long  

> way to say that the correction factors are only approximate in any  

> real world case.  If you calculate 100 ft of obstacle clearance,  

> turn back, please.  I'd want to calculate at least 1000 ft of  

> clearance, ideally even more.



 <sigh> Some people just get too literal. 


	


Well, I figured you probably knew that the calculation wasn't  

accurate enough to go with a 100 ft margin, but some other people on  

the list might not know that.



 	  Quote: 	
		   But all kidding aside, there really are significant errors and they  

 get worse as you go up and the temp differs from ISA. But you do  

 only need OAT and p-alt to get the correction factor. Does the  

 Rocky Mountain uEncoder provide true altitude? Ah, I see that it  

 does. Seems like a good thing.


	


Yes, you can get an approximate correction factor (emphasis on the  

word approximate) with one OAT and a pressure altitude.  But, the  

temperature ratio to standard temperature is never a constant value  

over the altitude band from the airport to the aircraft.  When it is  

very cold, there is often a temperature inversion in the lower few  

hundred feet, with the temperature increasing with altitude.  This  

sort of thing really fouls up any correction that is based on a  

single OAT difference from ISA.



I agree that the uEncoder's "true altitude" function is a nice touch,  

but I wish they had chosen a different name.   The uEncoder "true  

altitude" will still be in error by several hundred feet in many real  

world situations.



A whole bunch more info on why corrections using a single OAT value  

are only an approximation:



http://mtp.jpl.nasa.gov/notes/altitude/AviationAltiudeScales.html

Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

chaztuna(at)adelphia.net
Guest

Posted: Sat Aug 12, 2006 2:39 pm Post subject: encoder approval

snipped



  	  Quote: 	
		  Given that more people are going for all-in-one PFDs like Dynon, et  

 al, one is going to want to have a cross-reference for altitude. This  

 means a display for your encoder. By having a second air-data device  

 with a display you can cross check with your PFD. Something to think  

 about.



 Brian Lloyd                         361 Catterline Way

 brian-yak AT lloyd DOT com          Folsom, CA 95630

 +1.916.367.2131 (voice)             +1.270.912.0788 (fax) 	


 Brian,

  The RMI uEncoder is a great addition for the need stated above. I gives you redundancy for all 3 primary instruments as well as an encoder which is tied to the altimeter function. It only takes up one 3.125" hole in the panel. It's also handy for simplifying your scan during "partial panel" practice.

 Charlie Kuss

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Sat Aug 12, 2006 4:05 pm Post subject: encoder approval

On Aug 12, 2006, at 6:22 PM, Charlie Kuss wrote:



 	  Quote: 	
		   Brian,

  The RMI uEncoder is a great addition for the need stated above. I  

 gives you redundancy for all 3 primary instruments as well as an  

 encoder which is tied to the altimeter function. It only takes up  

 one 3.125" hole in the panel. It's also handy for simplifying your  

 scan during "partial panel" practice.


	


It looks like a good instrument. The only problem with a digital  

display is that it makes it hard to see trends. With steam gauges or  

tapes, I get information from how fast they are moving, something  

hard to see with changing numbers.



Regardless, it does give you a lot of information in one hole. I  

think that if I had AoA to give me airspeed trends I wouldn't care.  

Something like the uEncoder combined with an electric AI and I would  

have good backup for a glass PFD.



 	  Quote: 	
		   Charlie Kuss


	


Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

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