Transponder Calibration

We know that a transponder must be calibrated every 2 years and signed off by a qualified avionics technician. I assume that if this is not done, the aircraft is unairworthy (maybe only in class B & C airspace where a transponder is required). I personally know of several pilots/owners who rarely seem to bother with this requirement. How serious is it? I think for IFR flying it is more serious, but it is also a requirement for VFR flying. Has anyone ever been ramp checked or been dinged for this? I don't believe you are required to carry the calibration documentation on the aircraft. No big deal here; I'm just curious.

Jim,

If an aircraft does not operate in airspace where a transponder is not required, and is not equipped with a transponder, the lack of a transponder obviously negates a need to check it.

If an aircraft has a transponder, irrespective of what airspace it is operated in, the transponder must be checked every two years per 14 CFR 91.413. The transponder must also be on to fly if installed in any airspace.

I think the chance of getting caught with an out of date transponder is very low; however a low chance of getting caught is a lousey excuse for not complying with a regulation.

What will happen, if the aircraft is involved in an accident or incident, the issue of flying with a transponder not complying with 14 CFR 91.413 will be added to the list of violations. The longer the list of non compliance, the deeper the doo-doo the operator is in.

Insurance requirements normally include that an operator have their aircraft in compliance with applicable regulations. If not, a claim can be denied. A claim will likely result in some looking into records and we know where that will end up.

In neither case does it matter if an accident or incident was caused by the lack of a transponder check.

On the practical side, a transponder can go wonky at any particular time for no particular reason. I had one go out of calibration within the two year period when the tower asked "Exactly what altitude are you at?" . The stupid thing was reporting an altitude about 2,000' higher than I was at, meaning about that height above pattern altitude. The experience caused me to periodically include a request from an ATC station for mode C readback. In the process of getting a wavier from Approach control to go get it fixed, I found that transponders going out of calibration is not a rare occurance.

A VFR check isn't as costly as an IFR check.

The calibration check goes in the aircraft logbook and that is not required to be on board.

Thanks for your good comments Dave.

Jim - just a thought or two - It’s not the transponder, but the altitude encoder and altimeter that are adjusted if necessary. The transponder output is checked. With the ADS-B system mandated now, it might be considered even more important by some, whether IFR or VFR, to do the mandated testing because the transponder & encoder are critical parts of that system. I also know of some experimental owners who don’t get it done every 2 years, and I admit that I’ve been guilty of forgetting to get it done before also. Agreed, it’s even more important in the IFR system. If you happen to bust an airspace or altitude restriction they might want to see your aircraft log book and would certainly be looking for things like that. In between biennial checks, I periodically ask the tower what they read my altitude as, and compare that to what my altimeter is reading… sort of a “self check”.

Thanks John for your response.
I agree with all these comments, and just to clarify my own situation, I have never failed to get the calibration done or even missed it by a few days. I'm pretty nerdy about stuff like this. The only reason I brought this up was to get some thoughts and ammo other than my own to justify my bugging of some acquaintances who treat it very lightly.