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altimeter encoder problem

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davidjoyce(at)doctors.org
Guest

Posted: Mon May 27, 2013 9:36 am Post subject: altimeter encoder problem

Bud, Today I have finally got round to removing my panel 

and tracing the wiring. I found a faulty connection in the 

middle row of the multiple small pin connector to my Blue 

Mountain EFIS, corresponding almost certainly to the A" 

pin, which activates over 6000 ft (as predicted by Mike 

Gregory). Having resoldered it everything now works 

precisely up to 10,000 ft Many thanks for your input. 

Regards, David

On Sun, 21 Apr 2013 16:11:50 -0400

  "Bud Yerly" <budyerly(at)msn.com> wrote:

[quote] David,

 Not that I am an expert on the 328, but we have a number 

flying successfully.  It is pretty much a plug and play 

piece of equipment.

 It sounds as if your altitude encoder is separate and 

not part of an EFIS.

 If it is encoding properly at low altitude or sea level, 

but not at altitude, then your wiring is sound, it is the 

encoder.  You can use your Z component of your GPS to 

verify that the rest of your static system is sound in 

flight.

 

 If the altitude encoding is in error as altitude 

increases only, then it is in the encoder static pot 

itself.  However, to be safe, check your pitot tube for 

the W34 black static port attached well and secure to the 

lower pitot tube also.  Any leak in the system 

(especially in the wing) will cause errors with speed and 

angle of attack.  Of course if the W34 is missing, your 

static system is hooked to a pitot source which is really 

bad.

 

 Ameriking encoders as well as ACK are quite reliable, 

but if they fail, which it sounds as if it has an 

internal static leak, you will need a proper pitot static 

check by a qualified avionics shop to verify.  

 

 A crude check is to disconnect the static line from the 

encoder and run it to a very light suction hand pump to 

check pressure vs readout.  Of course you will need the 

temp and atmospheric tables also to establish the proper 

QNH.  For the very brave, only connect the altimeter and 

encoder together with a static line and use a light duty 

vacuum hand pump to increase the altitude and verify the 

readout on the 328 display with the altimeter.  If you 

pull too much suction or leave the airspeed attached, you 

will break costly equipment.  So as you can see, it is 

best to just go to an avionics shop and get a proper 

checkout as they have the calibrated equipment to do the 

job quickly and correctly...  If you built your panel for 

easy removal, your avionics shop will appreciate it.

 

 Note to all, it is prudent to have the pitot static 

system verified prior to first flight, and every two 

years after that by a qualified avionics shop. 

 Altimeters, encoders, and EFIS systems do fail.  It is 

best to have them checked periodically.  For years, I 

have simply pulled one inch of vacuum on my static system 

and checked the altimeter at 1000 feet increase, and the 

airspeed increases to 135 KIAS, the Vertical Speed 

Indicator is checked for rate of climb and the entire 

system checked that it will hold for 60 seconds. 

 However, at altitude, our absolute indicators may have 

small leaks and lie to us.  I still do my 1000 foot check 

just as a security blanket, but insist on a proper 

certified pitot static check prior to first flight.

 

 

 

 Best Regards,

 Bud Yerly  

  ---

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davidjoyce(at)doctors.org
Guest

Posted: Mon May 27, 2013 9:40 am Post subject: altimeter encoder problem

Remi, Today I have taken off my panel and traced all the 

wiring to find a faulty connection on the A2 wire coming 

out of my EFIS. Now works perfectly up to 10,000ft tested. 

thanks for your help. David

On Mon, 22 Apr 2013 04:43:12 -0700

  "Remi Guerner" <air.guerner(at)orange.fr> wrote:

 	  Quote: 	
		   

<air.guerner(at)orange.fr>

 

 Hi David,

 I propose to share with you my personal experience on 

that subject :

 My aircraft was originally fitted with a Garmin GTX320 

and a Terra AT3000 encoder. After a few years flying, I 

started to experience altitude reporting problems. ATC 

was occasionally seeing me at 6000 ft or below ground 

level while I was flying  at 2000 ft AMSL. I was once 

wrongly accused of having busted the class A London TMA 

while I was flying well below the max allowed altitude. 

Then I reworked the wiring without success, then I had 

the encoder tested by an avionic shop and it was found to 

be ok. Then I borowed another GTX 320 from a frend for a 

few flights and the system was working ok. So the culprit 

was clearly the transponder which was intermittently 

reporting an altitude different from the one transmitted 

by the encoder.

 I have since installed a mode S GTX328, keeping the 

Terra encoder and it has been working fine for the last 

five years.

 Conclusion : in most of the cases the culprit is the 

altitude encoder but it could also be the transponder 

itself.

 I hope that helps.

 Regards

 Remi

F-PGKL

 

 

 

 

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budyerly(at)msn.com
Guest

Posted: Mon May 27, 2013 1:43 pm Post subject: altimeter encoder problem

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Way to go David.

 Nine times out of ten, it is a bad ground or broken pin connection.   It just takes time to troubleshoot.

  

 Bud

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Remi Guerner

Joined: 14 Dec 2010
Posts: 284

Posted: Mon May 27, 2013 11:53 pm Post subject: Re: altimeter encoder problem

Hi David,

Good to know you have solved the problem. Thank you for the update.

Remi

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