# TONS of low cost King Mode C's out there... opinions?

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#### pfarber

See a TON of King Mode C's for sale. Like sub $300 in working order. I guess a lot are coming out due to ADS-B upgrades? I know a lot of them are officially out of support, but there still are quite a few repair centers taking them for repair/certification. I really don't need ADS-B OUT, and the NEW KT-74 is a bargain compared to a used KT-76C and uAviontics Tailbeacon. Thoughts? #### Daleandee ##### Well-Known Member I have a Garmin 320A transponder. I believe (I'd have to look at wiring schematics to be sure) the wiring connector is the same for the Garmin 327 transponder. If so, there is a lot of easy replacements that can be had if the one I have should die. Along with that I installed the uAvionix EchoUAT with Skyfyx-EXT that was on sale for$1349.00. This was a great choice for me as the Echo unit gives me ADSB "in" as well as "out" and works flawlessly with the Garmin transponder ... and it was cheaper than anything else.

Of course I fly "experimental" because I'm experimenting!

#### pfarber

##### Well-Known Member
I picked up a Garmin 327 for $325. Generally the small price difference between a KT76 and a Garmin 327 makes it an easy choice. I definitely want to stay under$500 for mode C that would include a 24 month cert. Most shops seem to have flat rate repair prices as long as its not a 'major' repair'.

It seems that Garmins are a PITA and need to go to Garmin for repairs... I 100% do not want to get roped into a manufacturer price controlled kit

#### Daleandee

##### Well-Known Member
It seems that Garmins are a PITA and need to go to Garmin for repairs... I 100% do not want to get roped into a manufacturer price controlled kit
With most used transponders like we are discussing here being in the few hundred dollar range I believe I'd look to buy another instead of sending one for repairs unless I could get a guaranteed quote up front that made the cost of repairs reasonable and worth it. The repair might be a better option if there is a favorable warranty on the work.

As far as the Garmin stuff goes ... I'm not a Garmin fan but admittedly their stuff don't break too often.

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#### TFF

##### Well-Known Member
To be a little more complex, only repair stations can do transponder checks. Doesn’t matter if it’s one guy or a whole station, a designee of a company can only do it, not a mechanic; even though more than likely it will be an A&P. What you are after is someone who has the credentials to sign your logbook. They put it in their log book. I have seen it done right and I have seen it done wrong. As long as they sign. The KT76a is a mainstay of aviation; I would not put one in a new plane. A Garmin 327 updates you to late 1990s. KT76a late 70s? No way. Just sent a helicopter to get one changed out and ADSB.

#### pfarber

##### Well-Known Member
That's not how 91.413 tests work. A Transponder check, done every 24 months per 14 CFR Part 91.413, is done IN the plane, including the transponder, altitude encoder, and transponder antenna. It tests the system, including the static port connection to the transponder altitude encoder.

So nothing is sent anywhere - you bring the plane to a certified testing station (or sometimes, they travel to you with their equipment), and for anywhere from $125 -$200, you get an approval, good for 24 mo.

Appendix F to Part 43 - ATC Transponder Tests and Inspections

The ATC transponder tests required by § 91.413 of this chapter may be conducted using a bench check

Funny, it seems that I CAN do exactly what I said. Will I still need a pitot/static check? NO!!!!!! Because the pitot check is ONLY for IFR. The xponder part is 100% doable in the bench.

So give me a AMEN! for RTFM.

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#### pfarber

##### Well-Known Member
To be a little more complex, only repair stations can do transponder checks. Doesn’t matter if it’s one guy or a whole station, a designee of a company can only do it, not a mechanic; even though more than likely it will be an A&P. What you are after is someone who has the credentials to sign your logbook. They put it in their log book. I have seen it done right and I have seen it done wrong. As long as they sign. The KT76a is a mainstay of aviation; I would not put one in a new plane. A Garmin 327 updates you to late 1990s. KT76a late 70s? No way. Just sent a helicopter to get one changed out and ADSB.
I have no need for ADS-B, so 1970s tech fits the bill perfectly. If I do need ADSB, then I would still just to a tailbecon or something cheap.

#### Turd Ferguson

##### Well-Known Member
Can do a bench test for mode 3/A only. So effectively, for mode C you'll be paying for 2 xponder checks instead of one.

#### TFF

##### Well-Known Member
You may have no need but I expect the rules will change requiring it down the road. Big brother loves you.

#### pfarber

##### Well-Known Member
Can do a bench test for mode 3/A only. So effectively, for mode C you'll be paying for 2 xponder checks instead of one.
Every check done for the 24 month cert can be done on the bench.

Appendix F to Part 43 - ATC Transponder Tests and Inspections

The ATC transponder tests required by § 91.413 of this chapter may be conducted using a bench check or portable test equipment and must meet the requirements prescribed in paragraphs (a) through (j) of this appendix.

§ 91.413 ATC transponder tests and inspections.

(a) No persons may use an ATC transponder that is specified in 91.215(a),

§ 91.215 ATC transponder and altitude reporting equipment and use.

Link to an amendment published at 86 FR 4512, Jan. 15, 2021.

This amendment delayed to Apr. 21, 2021 at 86 FR 13629, Mar. 10, 2021.

(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).

For VFR, there is ZERO need for a pitot/static check. Av1ate is just a list of all required inspections and CFI's regurgitate it because CFIs are mostly bad at instructing.

So under part 43 the xpnder is tested in mode A/C/S and for VFR you do not need a pitot system check... ever.

If you are trying to say that the encoder is not tested... I agree. The output of the encoder is not tested because its easy enough to check... usually on the face of the xpndr, or using a breakout box to check the outputs, or simply asking ATC for your altitude in flight.

But AGAIN, there is no need to certify the encoder. If you can find me an FAR that required a SPECIFIC INTERVAL for the encoder to be certified then please tell me. The best I can find is 91.217:

(2) 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

(3) Unless the altimeters and digitizers in that equipment meet the standards of TSO-C10b and TSO-C88, respectively.

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#### TFF

##### Well-Known Member
You are correct that you do not need the pitot static test in its self, but you do have to gain altitude on the altimeter or the encoder. There are two ways. One is pitot static, the other is turning the Kollsman window knob if you have an encoding altimeter. So the person testing can turn the knob to let’s say 15,000 ft or hook up the pitot static box. Turning the Kollsman up is a hack way, but like I said you are looking for a piece of paper to say you are legal. The investment for the repair station is pretty high. The total equipment is around \$20,000 and it has to be accepted by the local FSDO on the certificate to even be usable, much less the yearly calibration. You might not want the services, but they are the required industry standards, not your whim to be cheap.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Looks like 91.413 (b) requires integrated system test following any installation or maintenance where data error could be introduced.