Isn’t it just a question of an extra certificate? During my recent annual on G-NODE, the engineer ran functional tests on the entire avionics stack – transponder, NAV/COM, VOR, ILS, ADF, DME, marker beacon receiver. By the way, the tests took less than an hour but involved about £10000 worth of specialised test equipment.
91.171 is the 30 day VOR check – a trivial exercise taking seconds in the air, costing nothing, and signed off by the pilot with his license number.
We have a VOR test frequency on the field so testing requires only that you push the plane out of the hangar. I did mine yesterday, and found it 5 degrees out. I’d like to get it spot on, even though the plane is operated VFR (and navigated by Foreflight & GPS)… so I have another ‘little job’. Yesterday was my day for that kind of thing – testing in the air indicated that I also need to completely redo the magnetic compass installation, which I can also check on the field using the compass rose. Those kinds of things do make life easier.
My last Mode C transponder check was $75 US and the guy came to my hangar. It needed a little tweak, and got it. For my N-registered plane an FAA repair station has to issue the paper, and it arrived in due course by mail.
By the way, the tests took less than an hour but involved about £10000 worth of specialised test equipment.
I think there is a version of the very popular IFR4000 which can do the whole lot, including Mode S
I’ve been trying to buy a used one but everybody knows what they are worth 
They go for about $4000 and above. A few years ago the USA shut down a base in the Middle East and a large number of them ended up on Ebay but I think they are all gone now.
So I “rent” somebody down the road with one, for £20. His one does VOR, LOC, GS and a few other bits.
A lot of avionics fitters have cheap versions which e.g. cannot emit the LOC and GS simultaneously. That is OK for old mechanical avionics (CDI,HSI) because they don’t care if one is INOP and still display the other, but an EHSI (like the Sandel 3500) will inhibit the GS if there is no LOC.
My last Mode C transponder check was $75 US
It is £500 ($750) here for a visiting check, £300 ($450) if you take your plane to them. Maybe a bit less in a few places… 
Last week, there were three different instruments involved in the tests – one for the transponder, one for the DME, and one for all the rest.
We operate a Cessna 172S with 155a radios.
As I understand the above we can purchase an exchange 165a and this will be a slide in replacement.
We don’t have a HSI so maybee we can exchange Com 1 and use this as the primary radio
Is this an Easa minor mod? is there any way to do this paper work on our own?
Can’t help you with the EASA paperwork issue (it would be positively outrageous if it was a Major mod, so don’t take that from any avionics shop at face value) but yes a 165A is a slot-in replacement for a 155A.
Two issues to watch:
Make sure you order a KX165A/8.33. I believe that a non-8.33 version may exist on the US market. I am pretty sure it did exist for the KX165 (non A).
As you point out, there can be an issue with replacing a KX155A that drives an HSI (via a KN72 converter, most likely). I never spent time chasing this down and simply put the 165A in the COM2 position.
Peter
On the face of it I can’t understand why the KX165A won’t work in the upper position, the HSI receives it’s VOR / LOC info from the 155 via a VOR/LOC converter, this is fed with a VOR composite signal from the 155 and converts it into signals to drive the HSI.
The same pin on the 165 is allocated to VOR composite as it allocated in the 155, your 165 is clearly putting out the correct VOR composite signal as you have had it working in the in the #2 position.
The advantage with the 165 is that it was intended to drive the HSI directly as the VOR/LOC converter is integral to the box ( the VOR composite pin is intended to drive an RMI VOR indicator ) you might like to consider changing the cables and remove the VOR/LOC converter and drive the HSI directly from the 165 but my first move would be to check that the VOR composite pin in the back of the #1 position is correctly engaged in the back of the rack as this pin not making a good connection is the only reason that I can think of for the 165 not working in the #1 position.
More 155/165 stuff.
The 165A comes in 760 @ 8.33 flavours so make sure that you get the correct version.
The 165A has not got an audio amp so unless you have an audio panel this is an issue, for those who only have one 155 fitted as these usually use the 155’s audio amp to feed the intercom or in single seat installations the pilots headset.
The Bendix/King UK representative in the UK was clueless about the differences between the units and at the Goodwood festival of Speed I did my best to educate him as to the need for a KX 155/155A 8.33 replacement that would be a slide in replacement for the KX155. I told him that if Bendix/ King don’t want to disappear from this end of the GA market they need to build the KX155A in 8.33 with and without GS and with14 & 28VDC power versions now.
I am told that Trig have seen the 8.33 mandate as an opportunity to do the same thing with a NAV/COM as they did with the Mode S transponder and we can expect a slide in replacement for the 155 from them in the near future, I’m sure that Bendix/King know the ball is in their court ( I and others have told them directly ) and also know that they have to act quickly or loose the market to Trig. I think if I was a director of Trig I would be considering the price for a buyout from Honeywell as this seems to be the only easy way for Bendix/King to hold on to this end of the market.
Yes I agree. I think the issue is that the KX155A has no config, whereas the KX165A has various parameters which can be configured (via some front panel button messing) and probably the default values for the output signal type are not right for a KX155A replacement where the 155A’s composite NAV output went into a KN72 to be decoded for the KI525 HSI. I did spend a little bit of time playing around with it but had better things to do…
You are absolutely right that anybody who has a 155A and a KN72 driving an HSI or CDI should chuck out the KN72 and rewire the HSI to work directly from the 165A’s NAV decoder. But this is more £££ to be thrown at somebody, and the area is often poorly accessible. Plus you then lose the option of sliding the old KX155A back in, if you kept it as a spare.
Personally I am long way down the road from all that, with the COM1/NAV1 box’s (155A) composite output driving the SN3500 EHSI which decodes it in firmware and drives the autopilot via its FCS output. The KN72 is gone.
A lot of avionics fitters have cheap versions which e.g. cannot emit the LOC and GS simultaneously. That is OK for old mechanical avionics (CDI,HSI) because they don’t care if one is INOP and still display the other, but an EHSI (like the Sandel 3500) will inhibit the GS if there is no LOC.
Agree you can get a indication on several indications. However it won’t do 90 AND/OR 150 Hz tone delete, or VAR or REF signal which is needed to check the flag circuit. As well receiver sensitivity is measured.
Some owners think these test are expensive. If they want to, they can sit next to me when I do these test, when you explain what your testing customers seem to get a better understanding.
By the way, the tests took less than an hour but involved about £10000 worth of specialised test equipment.
I think there is a version of the very popular IFR4000 which can do the whole lot, including Mode S
You won’t be anywhere near with £10000 for carry out avionics and pitot static test according MPS for General Aviation. At that price you just have a single basic tester. I do have and IFR-4000 as depicted, however these units also need expensive upgrades as indicated before, for example for 406 MHz ELT support. The IFR-4000 only does HF, VHF and lower part of UHF, it does not do transponder at all. I also use an IFR-6000 which looks the same, but is an additional unit for mode A/C transponder and DME. Also this units needed expensive upgrades for mode S for example and for traffic systems. Offcourse also a pitot static tester. These testers also require annual calibration which is quite expensive.
The £20 guy seems to be a real good price, does he have calibrated IFR-4000 / IFR-6000 / pitot static tester for that kind of money? This seems hard to believe to me, as you would loose money using the testers, as you won’t be able to make enough only for the calibrations.
To do a full test it requires for me about 1,5 – 2,5 hours depending on the equipment installed. This is all avionics all pitot static instruments.
