Transponder died -- smartest choice?

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Martymccasland

Pre-takeoff checklist
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M.McCasland
The KT76A in our A36 died. I bought a bench-tested unit from our shop with a 6 month warranty for $800 and it promptly died as well (works fine for about 2 hours then ATC can't see us despite the transmit light blinking away). To add salt to the wound, I lost the transponder on approach to Chicago Midway.

So, what's the smartest thing to do? The shop offered to credit the $800 toward a new Garmin 327 installed for $2500 - or - swap for another used model or an ADS-B unit.

We've played with ADS-B on hand-held units a few times and was under-whealmed. Totally preferred the XM Weather. Traffic sounds nice, but in using the Garmin GDL 39 ADS-B portable product, I just started ignoring it after spotting 4-5 planes at reasonable altitude (that I would think would be in view of radar since I was in view with ATC and ATC is calling them out to me) not showing up in the feed... Also thinking more/better options will be on the market in the next 6 years -- and the traffic at least would be better once everyone is mandated. So not too eager to spring for ADS-B if it can be helped.

So with all of that said, what's the smartest route with a flaky transponder? Go cheap with another used KT76A and hope it lasts, buy the Garmin 327, or something else?

Many thanks in advance.
 
Check the antenna first. Throwing new transponders at it will do no good if the antenna is bad.

I like the 330 with my Garmin 430.
 
The klystron tube in the kt76s are getting to end of life. I want nothing to do with ADS-B so I would do whatever other option there is. But that's just me...
 
kgruber said:
If it is pulse equipment, buy new.

Transponder
DME
Radar
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I understand the point. These electronics are pushed hard, when they transmit.

But how many people buy DME nowadays?

If you wanted to replace DME, could you buy used so cheaply that you wouldn't care much how long it lasts?
 
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I looked into the Bendix King KT74 a little more and have some caveat emptor things for others looking to save a little money with the "direct slide-in replacement" that gets you ADS-B compliant.

First called my local Bendix/King dealer. He bought a few KT 74 units, got ready to install, and was working through the paperwork when he was surprised to find the STC was not FAA approved yet. He called King and was told it would be a while so he returned the units.

So I called King directly just now and spoke to their sales department. Sales told me "all STCs have been approved for all aircraft". I asked a follow-up question the sales guy didn't know and he connected me to the technical service engineer for the transponders.

The tech-support engineer said "only a few airplanes have been approved for the STC". As of now that list various models of Mooney, Piper, Cessna. Beechcraft would be around September if the schedule holds. He further said the STC is required for connecting the transponder to WAAS GPS to get the ADS-B requirement.

Then, the tech support engineer said, "but the unit is no longer slide-in replaceable at that point". ???? He said to connect it to the WAAS GPS as per the STC, it requires a new tray from the old KT76/78/etc that has 2 connectors on it instead of one -- so the major benefit of it being "slide-in" is lost if you want the ADS-B ability.

He *even further* said on top of that, an approved air/ground switch would have to be bought separately for full ADS-B compliance. The air-ground switches are either connected to the GPS or the pitot tube to determine if the plane is in the air or on the ground and somehow switches data modes on the ADS-B Out -- and is legally required to be compliant.

Again this is directly from King.

So it seems the niche the KT74 is filling is just a Mode-S replacement now with $1000-1500+ of additional labor, a new tray, an approved STC, and an air-ground switch later to be ADS-B compliant....

Had 2 different shops tell me if you are wanting full ADS-B In and Out probably the cost effective and bulletproof route currently is to get a rock-solid transponder like a Garmin GTX-327 and add a Garmin GDL88 later to get both ADS-B In/Out... If you were only after ADS-B Out now, something like the King KT74 plus all the extras described above (when the STCs are approved) or a Garmin 330 -- yet by the time the King "extras" are added to meet the ADS-B requirements, there's really no price savings over the Garmin 330. Your choice becomes if you just like King or Garmin. The dollars are about the same.

Just trying to help others out going down this same road.
 
Martymccasland said:
Snip...

So with all of that said, what's the smartest route with a flaky transponder? Go cheap with another used KT76A and hope it lasts, buy the Garmin 327, or something else?

Many thanks in advance.
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If you want to buy a used transponder for $800, get a Garmin GTX 320. No cavity tube to degrade, all solid state.
 
Martymccasland said:
He *even further* said on top of that, an approved air/ground switch would have to be bought separately for full ADS-B compliance. The air-ground switches are either connected to the GPS or the pitot tube to determine if the plane is in the air or on the ground and somehow switches data modes on the ADS-B Out -- and is legally required to be compliant.
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First of hearing this, and it doesn't sound right to me. :confused: Since every ADS-B out system needs GPS data, why wouldn't that be handled internal to the ADS-B transmitter?

Like usual there is not an installation manual online from the manufacturer :rolleyes2:
 
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bnt83 said:
First of hearing this, and it doesn't sound right to me. :confused: Since every ADS-B out system needs GPS data, why wouldn't that be handled internal to the ADS-B transmitter?

Like usual there is not an installation manual online from the manufacturer :rolleyes2:
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Made no sense to me either since you are already plumbing into the GPS to the King transponder. However, I asked again to be sure, "So that's yet another box that's required." And the King engineer said, unequivocally, "yes".
 
From the Garmin GTX-330ES Install manual:


"The squat switch field may be set to either YES or NO. Selecting YES in this field sets the GTX330 to use squat switch to determine lift off. Selecting NO sets the GTX330 to use Automated Airborne Determination from other sources"

Note 2 on the wiring diagram says:

"squat switch IN intput allows automated start and stop of the flight timer and places the transponder in ground mode upon landing <stanby>"

Definitions:

Flight time: Displays the Flight Time, controlled by the START/STOP key or by one of the four airborne sources (squat switch, GPS ground speed recognition, or altitude increase) as configured during installation. Time begines when the GTX330 determine the aircraft is airborne.

With all that known, there should be no reason the KT74 would need an external air/ground switching device or I would consider it handicapped.

Edit: looks like the trig stuff requires external air-ground switching also. I'm guessing they didn't want to write software and create a work around like Garmin did.
 
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bnt83 said:
"Slide-in replacement" is often a BS sales pitch. The PS Engineering will work in a GMA340 tray however, some of the features need to be wired up to take full advantage of the new gizmo.


I hate the term "slide in" and how it's thrown around.
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What surprised me what how many third-party reviews there are out there on the KT74 that don't mention all these gotchas. Flying, AVWeb, etc. Guess King bought a good bit of advertising.

At least hats-off to the King(Honeywell) tech support engineer being clear and up-front out the STC, new tray, and air/ground switch requirement.
 
Martymccasland said:
What surprised me what how many third-party reviews there are out there on the KT74 that don't mention all these gotchas. Flying, AVWeb, etc. Guess King bought a good bit of advertising.

At least hats-off to the King(Honeywell) tech support engineer being clear and up-front out the STC, new tray, and air/ground switch requirement.
Click to expand...


Indeed.
 
I dug into this more and as far as I can tell there is NOT any FAA requirement that ADS-B out equipment have automatic air/ground mode switching. That may not agree with whatever garbage RTCA wrote into DO-260B, which TSO-C166b (virtually useless) references. RTCA DO-260B being a private document not found for free anywhere, I’m not going to cough up $800 to view it. FAR 91.227 ADS-B Out equipment performance requirements.DOES NOT specify parameters that would require air/ground mode switching.

The GTX-330ES has proprietary software to determine air/ground mode if the aircraft is not equipped with a squat switch, airspeed switch or some other switching device. No external hardware required to get automatic air/ground mode switching.

The Trig TT21/TT22, King KT74, REQUIRE an external switching device for automatic air/ground switching

Trig TT21/TT22 Installation Manual No. 00560-00 Rev AK says:
5.6.7 Squat Switch Input
The Squat switch input allows the transponder to automatically switch between Airborne and Ground modes, and affects both the Mode S reply behaviour and the ADS-B reporting behaviour. The input will be asserted when the voltage to ground is pulled below approximately 4 Volts. The logical sense of the input can be programmed to be either active low or active high.
On an aircraft with no appropriate squat switch circuit this input should be left unconnected, and the transponder programmed to ignore the input.
6.1.6 Squat Switch Source
The Squat switch input allows the transponder to automatically switch between Airborne and Ground modes, and to automatically start and stop the flight timer. The sense of the squat switch input can be selected using the rotary knob. If the squat switch input is not connected the “Not Connected” option must be selected.
 
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bnt83 said:
I dug into this more and as far as I can tell there is NOT any FAA requirement that ADS-B out equipment have automatic air/ground mode switching.
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Maybe it's an STC requirement for the King KT74 in some/all aircraft? The King engineer was not at all ambiguous about the item being required.


As far as what this switch (physical or built-in logic) is doing in any ADS-B installation, what's the purpose? To keep planes on the ground broadcasting ADS-B Out information and causing false collision alerts to overhead passing traffic? Something else?

Assuming further that this on/off switch is independent of Mode S reporting since fields like Atlanta, Midway, Memphis, etc. require the transponder fully on even for taxing so it can be tracked by ASDE-X radar? Is that correct?
 
This is AC20-165, http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC 20-165.pdf

DISCLAIMER


b.
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to install ADS-B Out equipment. However, if you use the means described in this AC, you must follow it entirely. [/FONT][/FONT][FONT=Times New Roman,Times New Roman]
[/FONT]
3-10. Air-Ground Considerations.
a. [FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]The length width code is required by 14 CFR § 91.227, and is only transmitted in the surface position message. Thus, to comply with the rule, the aircraft must automatically determine its air-ground status and transmit the surface position message, which includes the length width code, when on the ground. [/FONT][/FONT][FONT=Times New Roman,Times New Roman]
[/FONT]b. ​

​

[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]For aircraft with retractable landing gear, the air-ground status determination is typically provided through a landing gear weight-on-wheels switch. For aircraft that have fixed-gear, the ADS-B system must still be able to determine the air-ground status of the aircraft. Installations that provide a means to automatically determine air-ground status based on inputs from other aircraft sensors are acceptable if they are demonstrated to accurately detect the status. These algorithms should be tested and validated during the installation approval. [/FONT][/FONT][FONT=Times New Roman,Times New Roman]
[/FONT]Note 1[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]: We recommend that any automatic air-ground determination be more robust than just a simple comparison of ground speed to a single threshold value. Field experience has shown that this method can lead to false air-ground status. [/FONT][/FONT]

[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Note 2[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]: Manual selection of the air-ground status is not acceptable. [/FONT]
[/FONT][/FONT][/FONT]
​
 
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I guess some helicopters are screwed. With no squat switch, no groundspeed the only way to determine airbone in hover is altitude increase.
 
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Martymccasland said:
As far as what this switch (physical or built-in logic) is doing in any ADS-B installation, what's the purpose? To keep planes on the ground broadcasting ADS-B Out information and causing false collision alerts to overhead passing traffic? Something else?
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Note[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]: Historically, transponders have been turned on by the flight crew when entering the runway for takeoff and turned off or to standby when exiting the runway after landing. When ADS-B is integrated into a Mode S transponder the existing guidance for transponder operation must be updated to ensure the ADS-B is operating during airport surface movement operations.
[/FONT][/FONT]
 
Seems to me a altitude increasing and ground speed > Vs0 equals airborne, for helicopter Vs0 can be zero


Sent from my iPad using Tapatalk
 
I really like my KT76C. Don't know if it's a slide-in replacement for the -A. BTW, does anyone know if the -C has a solid state or tube final?

Thanks.
 
teejayevans said:
Seems to me a altitude increasing and ground speed > Vs0 equals airborne, for helicopter Vs0 can be zero


Sent from my iPad using Tapatalk
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That might work for a takeoff, but what about landing? Altitude not decreasing won't work.

Also FWIW, the original purpose of automatic air/ground switching of transponders was to disable squawking on the ground so as to eliminate false traffic alerts and surveillance radar clutter. But recently the FAA began requiring you to leave your transponder squawking on the ground at many airports and recommends disabling automatic switching. ADS-B would appear to add another dimension to that mess if automatic switching is required for that.

I'd also like to point out that many retractable airplanes (e.g. all Bonanzas and Barons) have the squat switch wired in a way that makes them useless for operating anything else.
 
bnt83 said:
"Slide-in replacement" is often a BS sales pitch. The PS Engineering will work in a GMA340 tray however, some of the features need to be wired up to take full advantage of the new gizmo.


I hate the term "slide in" and how it's thrown around.
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Dear Brian, with all due respect, please tell me ONE feature that needs to be wired up when replacing the GMA340 with a PMA8000B to get ALL of the new functionality of the PMA8000B or PMA8000BT?

I must tell you, your statement of "BS sales pitch" and then your reference to our audio panel NOT being 100% plug and play causes me concern.

I enthusiastically look forward to your response Brian.

Sincerely,
Mark Scheuer
Founder and CEO
PS Engineering, Inc.
 
mscheuer said:
Dear Brian, with all due respect, please tell me ONE feature that needs to be wired up when replacing the GMA340 with a PMA8000B to get ALL of the new functionality of the PMA8000B or PMA8000BT?

I must tell you, your statement of "BS sales pitch" and then your reference to our audio panel NOT being 100% plug and play causes me concern.

I enthusiastically look forward to your response Brian.

Sincerely,
Mark Scheuer
Founder and CEO
PS Engineering, Inc.
Click to expand...


Upon further review, I stand corrected and apologize. Comment removed. I must have mistaken something when comparing them.

Maybe foaming at the mouth and keyboard turrets got me :confused:
 
This thread just reinforces my decision to sit on the ADS-B sideline until this all plays out...


Sent using Tapatalk
 
Martymccasland said:
Maybe it's an STC requirement for the King KT74 in some/all aircraft? The King engineer was not at all ambiguous about the item being required.


As far as what this switch (physical or built-in logic) is doing in any ADS-B installation, what's the purpose? To keep planes on the ground broadcasting ADS-B Out information and causing false collision alerts to overhead passing traffic? Something else?

Assuming further that this on/off switch is independent of Mode S reporting since fields like Atlanta, Midway, Memphis, etc. require the transponder fully on even for taxing so it can be tracked by ASDE-X radar? Is that correct?[/QUOTE]


Yup.. Salt Lake City requires squawking on the ground too.. I rode down there in a friends trick homebuilt a while back and he "forget" to wire in the squat override switch....:eek:
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Marauder said:
This thread just reinforces my decision to sit on the ADS-B sideline until this all plays out...


Sent using Tapatalk
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I will hold off on ADS-B till I am forced into it, as the only reason the feds want it installed is for being able to send you a user fee bill for every flight..:mad2:
 
N801BH said:
I will hold off on ADS-B till I am forced into it, as the only reason the feds want it installed is for being able to send you a user fee bill for every flight..:mad2:
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Next thing you know the UN will be collecting a carbon tax on those ADS-B targets.

I think the European union already does something similar with emissions tracking for aircraft.
 
mscheuer said:
Dear Brian, with all due respect, please tell me ONE feature that needs to be wired up when replacing the GMA340 with a PMA8000B to get ALL of the new functionality of the PMA8000B or PMA8000BT?

I must tell you, your statement of "BS sales pitch" and then your reference to our audio panel NOT being 100% plug and play causes me concern.

I enthusiastically look forward to your response Brian.

Sincerely,
Mark Scheuer
Founder and CEO
PS Engineering, Inc.
Click to expand...


Mark,

WELCOME to POA!!!

It is great to see your posts, and I hope you stick around.

Your products are "top of the line" in aviation. My Cherokee has your PMA 7000B.
 
kgruber said:
Mark,

WELCOME to POA!!!

It is great to see your posts, and I hope you stick around.

Your products are "top of the line" in aviation. My Cherokee has your PMA 7000B.
Click to expand...

I agree..... Mark makes some outstanding stuff....

I LOVE my PS Engineering product.:yes::yes::)
 
Marauder said:
This thread just reinforces my decision to sit on the ADS-B sideline until this all plays out...


Sent using Tapatalk
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Yup, agreed. By nearing 2020, ADS-B is going to be an app you can get at the Apple store, it'll cost $20, and run just fine. ;)
 
Marauder said:
This thread just reinforces my decision to sit on the ADS-B sideline until this all plays out...


Sent using Tapatalk
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While I agree this is probably a smart (cheaper) thing to do, if your transponder dies tomorrow, what do you do? Pick up a cheap mode-c to get you to 2020 or bite the bullet? To tell you the truth, not sure which way I would go in 2014, in 2018 I would go with ADS-B compliant.
If you believe some of the avionics advertisements, you should upgrade now before the BIG push in 2020 :rofl:
 
Back to the original question. I had an old Narco xpdr that kept on working, but I came across a Garmin 327 for $1100 and bought it. It came out of a King Air and was being sold by the shop doing the upgrades. Install, part of other radio wiring, was pretty cheap.
 
mscheuer said:
Dear Brian, with all due respect, please tell me ONE feature that needs to be wired up when replacing the GMA340 with a PMA8000B to get ALL of the new functionality of the PMA8000B or PMA8000BT?

I must tell you, your statement of "BS sales pitch" and then your reference to our audio panel NOT being 100% plug and play causes me concern.

I enthusiastically look forward to your response Brian.

Sincerely,
Mark Scheuer
Founder and CEO
PS Engineering, Inc.
Click to expand...

Mark,

I believe I spoke with you at AOPA Summit last year in Fort Worth. After speaking with you I installed your PMA8000BT and I have been very impressed with it. Thanks again.

Chris
 
Arrow115 said:
Mark,

I believe I spoke with you at AOPA Summit last year in Fort Worth. After speaking with you I installed your PMA8000BT
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So what is Mark left with since you have his?
 
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