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Rv9APlane

Joined: 13 Apr 2008
Posts: 4
Location: Bakersfield, CA

Posted: Sun Apr 13, 2008 4:53 pm Post subject: Questions on avionics

Hi all,

I have a couple of basic questions I don't understand well:



1.  What does it mean to "cage" an attitude indicator?  I've never flown a plane that has had this option but I see it on some I'm considering for my homebuilt.



2.  I want a light IFR panel and have read some things about Mode S transponders.  Is there any advantage to having one over a Mode C other than the TIS capability?



3.  Is purchasing a separate encoder necessary?  I was planning on putting a Blue Mountain EFIS One in my plane (please no negative comments as I'm already committed), a Garmin 430W with a GI-106A CDI, and a Garmin 327 transponder (pending the answer to number 2 above) in my plane.  I see some avionics vendors packaging in a separate encoder but don't really understand why.



Thanks for your help

_________________
Bruce Peters
RV9A, Fuselage
Bakersfield, CA

douglist(at)macnauchtan.c
Guest

Posted: Sun Apr 13, 2008 6:30 pm Post subject: Questions on avionics

At 17:53 -0700 4/13/08, Rv9APlane wrote:

 	  Quote: 	
		  

1.  What does it mean to "cage" an attitude indicator?  I've never flown a plane that has had this option but I see it on some I'm considering for my homebuilt.


	


Gyros come in gimbals that allow the rotor to stay in a plane (That's a term of geometry here.) while the airplane moves around it.  When you cage a gyro you clamp the bearings in the gimbals so that the rotating wheel is held so that its axis turns with the airplane. You do it when you set a directional gyro and then release it.  Older attitude indicators could be made to lie by exceeding the limits of their gimbals and the two axes would line up with each other and the gyro would lock up and "tumble". Caging it would keep it from tumbling but would also make it unusable for flight.



 	  Quote: 	
		  2.  I want a light IFR panel and have read some things about Mode S transponders.  Is there any advantage to having one over a Mode C other than the TIS capability?


	


Mode ADS-B is coming. It's a political point but I'd not waste cash on mode -S when ADS-B may be required before you get much out of S.



 	  Quote: 	
		  3.  Is purchasing a separate encoder necessary?  I was planning on putting a Blue Mountain EFIS One in my plane (please no negative comments as I'm already committed), a Garmin 430W with a GI-106A CDI, and a Garmin 327 transponder (pending the answer to number 2 above) in my plane.  I see some avionics vendors packaging in a separate encoder but don't really understand why.


	


You need a barometric input for any of the transponder modes. GPS altitude won't cut it. So external or internal it has to be a pressure measuring device connected with a tube to the static system.

-- 



--> From the U S of A, the only socialist country that refuses to admit it. <--

Rv9APlane

Joined: 13 Apr 2008
Posts: 4
Location: Bakersfield, CA

Posted: Sun Apr 13, 2008 6:46 pm Post subject: Questions on avionics

Thanks Doug, I appreciate the help.



 On Sun, Apr 13, 2008 at 7:24 PM, Doug McNutt <douglist(at)macnauchtan.com (douglist(at)macnauchtan.com)> wrote:

 [quote]--> Avionics-List message posted by: Doug McNutt <douglist(at)macnauchtan.com (douglist(at)macnauchtan.com)>

  

At 17:53 -0700 4/13/08, Rv9APlane wrote:

 	  Quote: 	
		  --> Avionics-List message posted by: "Rv9APlane" <rv9aplane(at)gmail.com (rv9aplane(at)gmail.com)>


	


 >1.  What does it mean to "cage" an attitude indicator?  I've never flown a plane that has had this option but I see it on some I'm considering for my homebuilt.

Gyros come in gimbals that allow the rotor to stay in a plane (That's a term of geometry here.) while the airplane moves around it.  When you cage a gyro you clamp the bearings in the gimbals so that the rotating wheel is held so that its axis turns with the airplane. You do it when you set a directional gyro and then release it.  Older attitude indicators could be made to lie by exceeding the limits of their gimbals and the two axes would line up with each other and the gyro would lock up and "tumble". Caging it would keep it from tumbling but would also make it unusable for flight.

  

 	  Quote: 	
		  2.  I want a light IFR panel and have read some things about Mode S transponders.  Is there any advantage to having one over a Mode C other than the TIS capability?


	




Mode ADS-B is coming. It's a political point but I'd not waste cash on mode -S when ADS-B may be required before you get much out of S.

  

 	  Quote: 	
		  3.  Is purchasing a separate encoder necessary?  I was planning on putting a Blue Mountain EFIS One in my plane (please no negative comments as I'm already committed), a Garmin 430W with a GI-106A CDI, and a Garmin 327 transponder (pending the answer to number 2 above) in my plane.  I see some avionics vendors packaging in a separate encoder but don't really understand why.

 
	




You need a barometric input for any of the transponder modes. GPS altitude won't cut it. So external or internal it has to be a pressure measuring device connected with a tube to the static system.



 

--



--> From the U S of A, the only socialist country that refuses to admit it. <--

  

 



  [quote][b]

_________________
Bruce Peters
RV9A, Fuselage
Bakersfield, CA

rampil

Joined: 04 May 2007
Posts: 870

Posted: Mon Apr 14, 2008 3:38 am Post subject: Re: Questions on avionics

The encoder output from a Blue Mountain EFIS is a perfectly adequate 

barometric encoder derived from its air data system.

As long as it passes biannual inspection like any other encoder, it is 

legal and good to go.  My old G3 encoder always passed inspection

_________________
Ira N224XS

Rv9APlane

Joined: 13 Apr 2008
Posts: 4
Location: Bakersfield, CA

Posted: Mon Apr 14, 2008 6:49 pm Post subject: Questions on avionics

Thanks Ira, I appreciate the help!

  

 Bruce

 On Mon, Apr 14, 2008 at 4:38 AM, rampil <ira.rampil(at)gmail.com (ira.rampil(at)gmail.com)> wrote:

 [quote]--> Avionics-List message posted by: "rampil" <ira.rampil(at)gmail.com (ira.rampil(at)gmail.com)>

 

The encoder output from a Blue Mountain EFIS is a perfectly adequate

barometric encoder derived from its air data system.

As long as it passes biannual inspection like any other encoder, it is

legal and good to go.  My old G3 encoder always passed inspection

 

--------

Ira N224XS





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=176685#176685

  [quote][b]

_________________
Bruce Peters
RV9A, Fuselage
Bakersfield, CA

bakerocb

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

Posted: Tue Apr 15, 2008 4:42 am Post subject: Questions on avionics

4/15/2008



Hello Bruce, You wrote:



"1.  What does it mean to "cage" an attitude indicator?"



Some attitude indicators have a mechanical means to lock the gyro gimbals so 

that the gyro gimbals are held rigidly to the instrument case. This can 

serve two functions:



A) It can save wear and tear on the gyro if you are going to do some 

aerobatic manuevering and don't want the gyro to be moving around 

extensively as it tries to always show the proper aircraft attitude.



B) If the gyro has tumbled and one wants to erect it again to a proper 

attitude one can put the airplane in a level attitude, cage and then uncage 

the gyro, and it will then start indicating properly a level attitude from 

that new starting point.



"3.  Is purchasing a separate encoder necessary?.....I see some avionics 

vendors packaging

in a separate encoder but don't really understand why."



They are doing this because the altitude encoder in almost all of the EFIS 

being sold to the amateur built community are not TSO'd and therefore do not 

comply with FAR Sec 91.217 copied here:



"91.217: 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."



So you can see that an altitude encoder in use must meet either be TSO'd or 

comply with subparagraph (b) above.



Some people think that the encoder, altimeter, and transponder checks 

required every two years by FAR Sections 91.411 and 91.413 meet the 

requirements of subparagraph (b) above, but that is not the present position 

of FAA HQ. They prescribe a more elaborate, almost impossible to accomplish 

test.



So one solution to the problem created by having an EFIS with a non TSO'd 

altitude encoder installed in your airplane is to install and use a separate 

TSO'd altitude encoder.



If you want to read more on this subject go to the Matronic aeroelectric 

list archive and search for 91.217.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



PS: Some EFIS manufacturers will claim that their altitude encoder "meets 

TSO standards". Note that a claim of "meeting TSO standards" and being 

actually TSO'd are not the same thing. Ironically some of these non TSO'd 

altitude encoders are actually superior in performance and technology than 

the standards required by the TSO. The EFIS manufacturers have chosen not to 

obtain actual TSO approval for their altitude encoders because of the 

expense and bureaucratic burden involved.



------------------------------------------------



 	  Quote: 	
		   Time: 05:57:43 PM PST US

 Subject: Questions on avionics

 From: "Rv9APlane" <rv9aplane(at)gmail.com>

 Hi all,

 I have a couple of basic questions I don't understand well:



 1.  What does it mean to "cage" an attitude indicator?  I've never flown a 

 plane

 that has had this option but I see it on some I'm considering for my 

 homebuilt.



 2.  I want a light IFR panel and have read some things about Mode S 

 transponders.

 Is there any advantage to having one over a Mode C other than the TIS 

 capability?



 3.  Is purchasing a separate encoder necessary?  I was planning on putting 

 a Blue

 Mountain EFIS One in my plane (please no negative comments as I'm already 

 committed),

 a Garmin 430W with a GI-106A CDI, and a Garmin 327 transponder (pending

 the answer to number 2 above) in my plane.  I see some avionics vendors 

 packaging

 in a separate encoder but don't really understand why.



 Thanks for your help



 --------

 Bruce Peters

 RV9A, Fuselage

 Bakersfield, CA

bakerocb

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

Posted: Thu Apr 17, 2008 5:55 pm Post subject: Questions on avionics

4/17/2008



Hello Ira,



1) You wrote: "There is no requirement for TSO in owner built aircraft."**



2) FAR SEC 91.217 Says:



"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."



3) Please explain, with specific valid reference, why the phrase "No person 

may ..." seen above would not apply to a person flying an amateur built 

experimental aircraft.



4) You are correct that there are alternatives to using TSO'd equipment, 

when such equipment is specifically required by a regulation, provided that 

you can prove to the FAA's satisfaction that your alternative equipment is 

acceptable to the FAA. Here is how you go about doing that:



FAR Sec. 21.609   "Approval for deviation.



(a) Each manufacturer who requests approval to deviate from any performance 

standard of a TSO shall show that the standards from which a deviation is 

requested are compensated for by factors or design features providing an 

equivalent level of safety.

(b) The request for approval to deviate, together with all pertinent data, 

must be submitted to the Manager of the Aircraft Certification Office for 

the geographic area in which the manufacturer is located. If the article is 

manufactured in another country, the request for approval to deviate, 

together with all pertinent data, must be submitted through the civil 

aviation authority in that country to the FAA."



Obtaining an approval for deviation is not a trivial task and none of the 

manufacturers of non TSO'd altitude encoders contained in their EFIS units 

have done so to my knowledge.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



**PS: This statement is also not correct when it comes to the ELT installed, 

if one is required by FAR Sec 91.207, in an amateur built experimental 

aircraft.



-----------------------------------------------------------------



Time: 04:30:41 AM PST US

Subject: Re: Questions on avionics

From: "rampil" <ira.rampil(at)gmail.com>

      Re: TSO and altimetry sources



      There is no requirement for TSO in owner built aircraft. As I said

      previously, there is only a performance requirement.



      Part 23 is a separate issue.



      --------

      Ira N224XS

bakerocb

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

Posted: Sat Apr 19, 2008 4:15 am Post subject: Questions on avionics

4/19/2008



Hello Ira, You wrote: "........I was referring to encoding altimeters when I 

said there

was no requirement for TSO."



If that encoding altimeter is the altitude encoder that is feeding the 

transponder required by FAR Sec 91.215 then it must comply with either 

91.217 (b) or (c). That is what this thread has been about.



See my response to Mike, copied below, for more information.



'OC'



-------------------------------------------------------------



4/18/2008



Hello Mike, Thanks for your three emails. You wrote:



1) "....you are looking to comply with the standard of the TSO without a

formal

proof."



A) I invite you to look at "Subpart O -- TSO Authorizations" of FAR Part 21.

You can access it here:



http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9dad7a792e03c09e14fc110ded0921cb&rgn=div6&view=text&node=14:1.0.1.3.9.15&idno=14



B) Then I invite you to look at TSO-C10b. You can access it here:



http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgTSO.nsf/0/072c91c58fdc6ce686256da4005f4d1b/$FILE/C10b.pdf



C) Then I invite you to look at TSO-C88b. You can access it here:



http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgTSO.nsf/0/625ebf9767dac15e8625727c006e10df/$FILE/TSO-C88b.pdf



D) Now I invite you (and here is the gotcha) to procure and look at all the

technical references contained in those TSO's. The TSO's themselves are just

sort of shell documents, pointers if you will. All the real technical guts

and standards that must be complied with are found in the references.



E) Now I ask you to picture the average homebuilder satisfying someone that

he is complying with the standards of the relevant TSO's without formal

proof.



2) "It says that the 'encoder' must meet the TSO standards.  It doesn't say

that it must be TSO'd.  That is a subtle legal difference."



I accept your "subtle legal difference". After you have gone through steps A

through D above I ask you to picture the average homebuilder satisfying

someone that his non TSO'd altitude encoder is meeting the standards of the

relevant TSO's .



3) "So answer me this:  If you the builder /manufacturer determines that

your testing puts the encoder in compliances with the TSO standards......."



Again I ask you to picture the average amateur builder determining that his

testing puts the encoder in compliance with the TSO standards -- not some of

the standards, not just the performance standards, but the all of the TSO

standards. The reason that the EFIS manufacturers have not done this very

thing is because of the significant cost and bureacratic burden involved.



4) "...and you test the unit IAW 43.13 and it passes ......"



A) (I am not sure why you referenced 43.13. It does not appear to be

relevant here. Perhaps you meant FAR Sec 91.413. I will assume so.)



First off I, the amateur builder, am not permitted to perform the tests

required by 91.413 -- see sub paragraph (c) of 91.413.



B) "......what would be the ramifications?"



Second, assuming the tests required by 91.413 were properly performed by a

willing qualified person / entity, the automatic pressure altitude reporting

equipment containing the non TSO'd altitude encoder passed the tests, and

the test results were properly documented there probably would be no adverse

ramifications. But consider this:



B-1) Suppose a willing qualified person / entity is not readily available to

perform the 91.413 required tests because the non TSO'd altitude encoder is

not in compliance with 91.217? What are the ramifications then? Probably no

big deal, go find someone or some place that will perform the tests.



B-2) Suppose that there is a mid air collision between an amateur built

experimental aircraft and an airline aircraft with major loss of life. And

further suppose that the equipment in the amateur built experimental

aircraft had absolutely nothing to do with causing the accident, but the

media learns that the amateur built experimenal aircraft was not in

compliance with some Federal Aviation Regulation (91.217) . What are the

ramifications then?



5) "I don't see a violation of the rule as written."



I am not sure which rule you are referring to. If you are referring to

91.217 there are two choices:



A) Comply with subparagraph (c); ie have equipment that is TSO'd, or



B) Comply with the tests described in subparagraph (b). I think that the

tests required by 91.411 and 91.413 should be considered to meet the

requirements of 91.217 (b). Unfortunately, to date the FAA HQ does not agree

with me and they seem to have  a little more authority than I do.



6) "Also their is no enforcement mechanism in place to even determine

whether your in compliance or not."



True enough. I think the FAA is too busy measuring the spacing between

lacings on wire bundles in the wheel wells of airliners to make very many

ramp checks on the avionics installed in amateur built experimental

aircraft, but see the ramifications comments above and make an informed

decision.



7) "You as the aircraft certifying authority as the builder......"



The Special Airworthiness Certificate in the Experimental Category for the

purpose of Operating Amateur Built Aircraft is signed and issued by an FAA

Representative who has been delegated that authority by the FAA

Administrator. The FAA Administrator is the certifying authority, not the

amateur builder.



 "You ........ as the builder determine suitability as it pertains to the

regulations and no one else"



Try telling that to the FAA employee or DAR who comes to inspect your

amateur built experimental aircraft for its initial airworthiness

inspection. He will set you straight very quickly on who will make the

decisions regarding the suitability of your aircraft as it pertains to

regulations.



9) "Short of them scouring the wreckage for TSO tags they would have to make

an assumption."



I hope that it would never come to that, but the tenacity, search for

details, and the ill will of lawyers and journalists when they smell blood

and money should not be ignored. All I am seeking to do is to have people

make informed decisions -- I provide the information, they make the

decisions.



'OC' Says: "The best investment we can make is the effort to gather and

understand knowledge."



-------------------------------------



Time: 08:28:34 PM PST US

From: "Mike" <mlas(at)cox.net>

Subject: RE: AeroElectric-List: Questions on avionics



I would argue that you are not looking for a deviation to the TSO you

are looking to comply with the standard of the TSO without a formal

proof.



Mike



-----------------------------------------------------

Time: 08:34:11 PM PST US

From: "Mike" <mlas(at)cox.net>

Subject: RE: AeroElectric-List: Questions on avionics

Read the regulation.  It says that the 'encoder' must meet the TSO

standards.  It doesn't say that it must be TSO'd.  That is a subtle

legal difference.



Mike



-----------------------------------------------------



---

douglas.dodson(at)pobox.c
Guest

Posted: Sat Apr 19, 2008 8:06 am Post subject: Questions on avionics

This discussion is symptomatic of what is driving light aircraft GA into

oblivion.  If I get my transponder static check done and it passes, then

the system works today.  I suppose it could break tomorrow, but so could

one that "legally" meets the TSO.  At least I can afford to fix mine

since the engineers didn't have to pay any lawyers.



- Doug



--

bakerocb

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

Posted: Sun Apr 20, 2008 4:55 am Post subject: Questions on avionics

4/20/2008



Hello Ira, You wrote:



1) "This is just the performance test."



I assume that you mean the testing required every two years by FAR Sec's 

91.411 and 91.413 as appropriate.



I apologize for not having made the situation clearer to you. I also wanted 

the testing required by 91.411 /  91.413 to sufficiently meet the 

requirements of 91.217 (b) so that one could operate with an EFIS that 

contained the only atitude encoder in the airplane and that altitude encoder 

would be non TSO'd. So I wrote to FAA HQ asking that question. Here is an 

exact quote of their response:



"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."



So you can see that FAA HQ does not agree with our wishes. Further you can 

see that an amateur builder attempting to comply with the FAA HQ version of 

the testing requirements of 91.217 (b) in order to avoid having a TSO'd 

altitude encoder installed in his airplane would have a very difficult / 

impossible time doing so.



2) "It says nothing about TSO."



That is correct. The TSO part is found in 91.217 (c). So the person 

mentioned in the beginning of 91.217 is given two choices -- he can comply 

with either 91.217 (b) or (c).



3) "Part 21 and 23 do not apply to owner built aircraft with special 

airworthiness certificates."



Basically true, but not specifically relevant to this discussion unless the 

builder would try to use a non TSO'd altitude encoder by requesting approval 

to deviate from TSO C-88b and its references in accordance with the 

procedures of FAR Sec 21.609 -- not a trivial task.



Please let me know if I have not adequately described the situation.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



-----------------------------------------------



Time: 07:01:52 AM PST US

Subject: AeroElectric-List: Re: Questions on avionics

From: "rampil" <ira.rampil(at)gmail.com>

Again, back to 91.217 (b):



(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



This is just the performance test.  It says nothing about TSO.

Part 21 and 23 do not apply to owner built aircraft with special

airworthiness certificates



--------

Ira N224XS

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