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New owner light IFR avionics questions (UK)


Just did my first flight in my shared 172, and I was wondering if anyone can recommend how to go about the following set of fixes done, in the UK. The aim to get the aircraft equipped for light IMC. The majority of owners have either an IMC / IR(R) or plan to get one, but the aim is to deal with the usual UK murk; we don’t have an illusions about a 172 being a hard, or even moderate, IFR machine, and we don’t have an autopilot in any case.

1) We’ve got a GNS430W. It needs the software updated, and we’d like to buy a database update (probably just one per year). I’ve read a few threads on this – we need a card reader, a spare card (preferably) and a copy of the database itself. It would be lovely if we could borrow at least the card reader from someone.

2) Our KN64 DME has just died. It might just be the display but is it even worth trying to repair it, or should be replace it? We’ve got a GI106A CDI installed, so it’s a real problem to no longer have a DME to go with our ILS (unless we can use the 430W?)

3) We’ve only got a vacuum AH. We want an electrical one as I’m not comfortable flying IMC without one. I’m considering just putting a Dynon D3 into one of the empty spaces, but we’re also considering a GI275. Thoughts?



Denham, Elstree, United Kingdom

@Winston for practical purposes the 430W with an updated database can provide range on an ILS (and would be legal in the USA, assuming you loaded the approach, and not used a simple waypoint), and legal in the UK, in a radar environment. Radar will advise range for the GS check, and provide missed approach instructions understanding that you are not ADF/DME equipped.

If you want a working standby AI then a D3 seems perfectly workable.

Starting the journey to upgrading your panel to TAA equivalence (2 axis AP, dual GI275) you will soon enter £20k plus territory, before you decide to upgrade the 430W. The installation, and add ons, of the GI275 needs careful scope and budgeting. At this point finding an aircraft which already has an updated panel might make more sense?

Remember the IRR is a safety rating, and ideally, if used in anger, the let down could just be a radar vector to a cloud break subject to MSA. A radio, transponder and VOR/ILS being perfectly adequate.

Oxford (EGTK), United Kingdom

@RobertL18C thank you.

Sounds like good news on the DME front – for getting home Southend or Oxford would be my likely alternates so that’s good. Not sure Biggin would work as I can’t image Thames would want anything to do with us. The ADF display has lost a digit as well, but we’re going to leave that to rot.

I asked about the GI275 as one of the other owners mentioned it. I’m skeptical what it gives us beyond the D3 in an empty hole for a fraction of the cost.

There’s no ambition to fit an autopilot. If I were waving a magic money wand I might want to put in a slaved DG or even a HSI as I rather like them, but there’s no rush on that.

Noted on the IRR – the aim here is to equip the aircraft to let us do a let-down safely, and avoid scud-running near terrain. It sounds like the 430 update and the D3 are the only things we really need to meet that right now.

Thanks again.

Denham, Elstree, United Kingdom

Whether it’s ‘light IFR’ or some other kind of IFR, the 172 doesn’t care
Properly rigged and in calm air or general bumps, can be hand flown in IMC for a couple of hours if necessary. But if you’re IFR, updating the database a couple of times a year just isn’t an option.
I’d be happy with a D3 as backup and have one, but remember it needs to be set up each flight which can be a bit annoying compared to a second panel mounted electric unit.

Personally I use a DME quite a lot (probably an old learned method I can’t quite shake)
Even though information is available on the 430, I like to glance down and see a reference distance to whatever beaco I’ve tuned.
If mine failed I’d have someone looking at it within a couple of days.

United Kingdom

Winston wrote:

we’d like to buy a database update (probably just one per year)

Note that you may not use the navigator for primary navigation if the database has expired since more than 28 days. If it has expired at all you need to check before flight that routes and waypoints you intend to use have not been changed. (AMC2 to NCO.GEN.105.)

Also, you may not use an expired database for PBN approaches, SIDs or STARs. (AMC2 to NCO.OP.116.)

A database subscription is not all that expensive.

ESKC (Uppsala/Sundbro), Sweden

Thanks, @GA_Pete and @Airborne_Again. I’ve not started my IR ( R ) so I’m glad you’ve told me about the database updates. It’s not that expensive in the scale of things, but perhaps I had been hoping that for IFR outside CAS in the UK flying the occasional ILS we might have gotten away with less frequent updates.

Having slept on it my feeling is that we need either the DME fixed or the database to be up-to-date (preferably both).

Re PBN approaches, as we don’t have any full IR in the group, we can only fly IFR in the UK, and not in class A. PBN approaches are, errr… sparse in the UK and EGNOS just went away (legally, at least). I also can’t see a Cessna 172 flying many SIDs or STARs in the UK.

As discussed earlier the aim here is not to plan to fly in IMC, but to have the equipment deal with it safety and make an approach, probably as a diversion when the destination turns out not to be VMC.

Thanks again – much to learn.

Denham, Elstree, United Kingdom

Winston wrote:

As discussed earlier the aim here is not to plan to fly in IMC, but to have the equipment deal with it safety and make an approach, probably as a diversion when the destination turns out not to be VMC.

If you expect to only make ILS or VOR approaches, then of course the database doesn’t matter.

ESKC (Uppsala/Sundbro), Sweden

Hello Winston,

first of all congrats to becoming an owner.

The GNS430W is still a very valid and powerful navigator. If you consider IFR at all, be it IMC or IFR even enroute, the database should get updated on a monthly basis. It is not a big deal in the context of flying (about 400 Euros p.a.) and if you have your own Skybound USB device it is a story of 10 minutes. Particularly if you are not flying regularly, I’d find it rather disturbing if you fly with an expired database and are sent to a non-existent waypoint or to a procedure which your GNS does not have because of this.

DME: If you have a good and reliable avionics shop I’d hand it in for an evaluation what is broken. I had a similar situation with a device where forum wisdom talked of several thousand worth of repair but the guy in my avionic shop found the mistake quickly and repaired it for very few money. KN64’s are also available on e-bay often enough, if a repair is too expensive, a swap out unit may be cheaper.

As for an electrical ADI, there are quite nice options today, which really increase the amount of information you have. Be it a G5, one of the cheaper Aspen PFD’s or the GI275. I love my Aspen for many reasons, but I see the G5 and particularly the GI275 as pretty powerful instruments too. Eventually you might even want to go the “non-vaccum” way, going with something which is newer and likely to be available for further upgrades later on may be a good idea.

The Dynon D3 is also a quite powerful device. I own a D1 myself for the very purpose of a backup to the backup. What I find problematic with those is that they show GPS altitude and Groundspeed in a setting which is actually suggesting IAS and normal altitude. Hence I think these devices really are only usable for attitude information (and in the case of the D3 the synthetic terrain). And while it can safe your bacon if all your gyros / EFIS die in IMC, I would not compare it to any of the proper ADI’s like a G5, a GI275 or an Aspen.

LSZH(work) LSZF (GA base), Switzerland

I have flown IFR in UK on IMCr with KNS80 (we had a legacy GPS that is now VFR only) before upgrading to GTN, first there are not that many VOR/DME approaches, so you will be mostly flying ILS & LOC approaches (or few VOR cruise, climbs, descents to MSA or somewhere nice)

In theory 2*VOR/DME or better a KNS80 should get you RNAV5 in UK bellow FL95 (equipment needs to be FM immune and some caveats on how you file FPL), you can fly OCAS and few airways (Class E on IMCr or Class A on IR) with barely that but you can’t fly SID & STAR, they are RNP1 and they needs IFR GPS (we rarely have these in GA airports, maybe except Cardiff Brecon departure, which will takes you in Class A ) but you won’t count on this for very long as most en-route flying under radar is done tragically on radar vectors & waypoint directs, refusing directs will make you a very popular guy

You definitely need moving map (SkyDemon) for situational awareness while doing UK IFR OCAS flying and be careful with directs on GPS, following TO/FROM radials on VOR OBS, tracking & homing on NDB only fly your printed plog with properly planned routes & altitude, written radials and nailing the heading or just don’t go up and see how it goes, you will hit the jackpot: entering airspace without permission is criminal offense these days, doing that while flying SEP in weather and not talking to the right guys (and we don’t talk to TMA ATC) adds more reckless element to it !

Also note IMCr off-airways flying with no autopilot on legacy instrument while dealing with complex airspace and harsh weather is the hardest form of flying, anything else is piece of cake (say VMC on top at 12kft with full IR in Alpha or VFR on sunny days bellow 3kft), so careful planning is a must, you need few hours on the ground for planning: study route, listing frequencies, headings, altitudes and budget time for zillions of RT calls, don’t go freestyle !

You don’t need PBN for IMCr but I suggest reading “PPLIR PBN manual”, use PC trainers & simulators to practice and play a lot in VMC inside the aircraft to know your GPS (it’s your life after all ), the typical IMCr/IRI instructors don’t know much on the topic of GPS because they like you to fly on legacy instruments locally or in VMC, if you find one who use GPS in aircraft for real you may learn one or two things

Last Edited by Ibra at 24 Jul 10:06
Paris/Essex, France/UK, United Kingdom


@Winston, DME is good if you need to land at a place with no radar (EGMD/Lydd) or it is just switched off (EGSC/Cambridge, sometimes EGMC/Southend!).
RNP IAPs – Shoreham, Sywell, the other runway at Lydd or Cambridge.
And even if you don’t plan to fly actively IFR now, it does not mean you wouldn’t in the near future! :)
Even with IR you can get out of EGTR at 2100AMSL when the cloud base is say 1300AGL (1600AMSL) and then climb above the cloud layer later, when TMA gets higher, and then, for example, cross the Channel VFR on top at, say, FL55.

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