RNAV Approaches on a Budget

MBDiagMan

MBDiagMan

Final Approach
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Mount Pleasant,Texas
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They recently decommissioned the VOR near my home field. My Mooney is properly equipped with a 430 W and the RNAV approaches into my home field are no problem. My little taildragger OTOH has dual VORs with a glide slope. I keep it around because it’s fun to sight see over the lakes and is great for running short distance errands including a weekly trip to check on my small ranch a few counties away. The VOR near that field is scheduled to decommission soon.

My little taildragger has a nice panel given the time period it was built, 1980. I can’t justify a 430, even non WAAS. It has a good set of radios, so I’ve been thinking about adding another antique to the panel. I can get a GPS155 XL pretty cheap. If I had a CDI in place to use that would be the end of the equipment expense, but the VOR’s are Narco 121 and 122 which are self contained NAV radios. I would remove the 121 which is a Localizer only and leave the 122. The 121 would be replaced with a CDI for the 155.

There is room in the stack. If I moved the checklist panel on the bottom it would be an easy installation, but having it so low I think would be a problem. The other option would be to put the 155 in place of the top COM, move the top COM below the one that is now second from top and move the transponder below that. That would be a big job for which I would have to delegate to the avionics shop.

8112806E-364C-482F-95AE-99C33F4CE475.jpeg
 
I generally like the 155 Idea. But might consider the total cost of the 155 including installation and the CDI vs a 175 with either a CDI or G5 HSI. The cost difference in the end might not be that much,

Brian
CFIIG/ASEL
 
Your biggest risks with a vintage GPS will be database availability and support/repairs. Given that you'll be spending at least $5K on installation either way, saving a couple of AMUs by buying an ancient 155 instead of a modern $5K 175 might not make sense. If you do go the used route, make sure you're getting the tray, harness, and antenna with the unit.
 
Would you have room for a CNX80?

We have removed the one out of Skylane and will be putting it up for sale...

PA. we need to planning some flying together!
 
One way of doing it while avoiding panel surgery is to yank both NAV's and 1 COM. GPS goes where the COM used to be, Trig TY91 (COM) replaces one NAV and a Val INS 429 (NAV with both internal and external CDI capability) replaces the other NAV. GPS gets wired to the Val, which has internal switching capability.

However, it might be more than you want to spend and the Val becomes a single point of failure.

Or you could spend a little more for a GPS/COM like a 300XL or a GNC355.
 
bbchien said:
Wow. An IFR Cessna 140!
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There's no limit to human ambition. ;)

Circa 1990 I was wandering around the ultralight grass runway area at Oshkosh and came across a McCulloch powered pusher with a Loran in the panel.
 
What’s your budget? I might have a GNC-420 that could fit your needs.
 
bbchien said:
Wow. An IFR Cessna 140!
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Dr. Chien,

It is and has been IFR since its restoration in 1980 with the custom, state of the art panel of its time. It’s just that now I want to do RNAV approaches.

The history of the plane is that the restoration and modification was done at great expense by a previous owner who gave it to his wife for her birthday and she got her instrument rating in it. That was 40 years ago. The plane has been hangared and well cared for ever since.
 
One of the reasons I hadn’t seriously considered replacing Com1 with a GPS was that the existing radio is 1 3/4” tall while the GPS155XL is 2” tall. In looking closely at my picture I remembered that there is a filler panel below COM1. That indicates that a 2” tall tray could fit in that position. That means I could put a 300XL there, use it for COM1 and have a spare radio on the shelf for the COM2 position. That still means there is the expense of a CDI which would replace the NAV2. I would then move the glide slope NAV down to NAV2 position and put the indicator on top.
 
Don't forget, the 155 needs that (small) annunciator/button unit as well, maybe 1.5 x 3.5" or so, and, I'm not sure, but there's probably specs on how close to the pilot it must be installed (Like, over on the right in your glove-box probably won't meet the spec.)
And, though I fully understand the stance on not wanting to install a newer box, FWIW, I'd vote to wait till the piggy bank gets full and install something newer. Who knows how long before Garmin drops support for those older units, or you can't even update the database, etc.
 
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MBDiagMan said:
Is an annunciation panel necessary if the CDI is dedicated to the GPS and not shared with a NAV?
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It's my understanding that the annunciator is required for IFR use. Besides the NAV/GPS switch, it also has the required Approach activate and sequence/hold/suspend buttons that are not available on the GPS unit itself like they are on the 430 or 650 etc.
 
AggieMike88 said:
Would you have room for a CNX80?

We have removed the one out of Skylane and will be putting it up for sale...

PA. we need to planning some flying together!
Click to expand...

As far as size goes, it would cause me to completely rebuild the stack. It doesn’t fit my budget either.

.... and yes, we do need to get in some flying.
 
How budget is budget?
A 175 is a bone-simple install, move your transponder down 2" and slide it in there. The indicator would be right next to it, so minimal work behind the panel. Mine's about that level and is fine. If you need annunciators , two light bulbs do the trick. Current gen technology is worth the little extra $.

Shop hard and you can find one under $4k. Good used indicators can be found under $1 ,5k. If you have a helpful A&P, the install is cake.
 
I’d suggest the GPS 175 or the GNC 355. Going with something like the 300XL or other stuff, you are already out of any sort of repair support for the units and who knows how long for database support. At least with a 430 there is still repair capability for some period of time and database support will likely be around for a looong time due to install base. Could maybe also sell the ESG, and install a 375, re-use the antenna. It’s too bad the ESG can’t take position source over serial, so you have to install another antenna.
 
saw a GPS175 on either barnstormers or ebay for under four grand... that's alot more than budget stuf, but it's alot of NEW garmin technology, supported into the future, works well with an ipad, etc., etc. expensive, may be well worth it.
 
Doug Reid said:
Is that a filler panel behind your checklist ?
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Yes, the checklist is on a filler panel. All that real estate is available for expansion. I really don’t want a navigator down there though. It would be too hard to see. Things in the stack would have to be shifted.
 
Now if we could just find you a WAAS cat and and RNAV duck....
 
Reason I asked...if you have a little slack, you might be able to lower the entire stack and install your gps below the audio panel...a lot of if's....yoke clearance , etc. Good luck.
 
There appears to be enough slack to move everything down 2 inches.

I flew an approach this afternoon in a friends plane with a 300 XL. Without glide slope it was a little ragged, but I believe a little practice and I could fly a pretty good non precision RNAV approach with it. It sure beats having no way at all to get in my home airport.

I suspect that the 155XL is the same unit without the radio. It would be much easier to install to a point that I expect I could install it myself. Lower the stack and put it below the audio panel. Does it also require an annunciator?
 
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Well, maybe so, but I found a 155, antenna and CDI for $1200. Would have to find an annunciator. That’s a pretty significantly different equipment cost than a 175. That said, the 175 would bring WAAS and precision approaches along in the bargain, but I can take up a couple thousand bucks pretty easy and don’t mind putting that much into a plane that’s not worth much. Coming up with $5700 OTOH would be a different kettle of fish.
 
I am in similar situation here...they did away with our VOR approach...but the GSO VOR is still active. Only GPS approaches into my home airport now.

BTW, I suppose you know you can download install manuals for the ESG and 155xl..good luck...keep us posted.
 
new GPS 175 for 4095 and a used ki209 picked one up for 300 bucks. The install cost will be the same as your old tech. the 175 will not need annunciator if located in the pilots angle of view.

https://avionics-laf.com

find the 175 and put it in the cart to see sales price. They ship free to texas and no sales tax. I purchased a GTR225 from them
 
MBDiagMan said:
It has a bunch of wires out of a big connector so I think it’s safe to say it’s not a serial connection. Can it drive the Appareo AND the 155XL?
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From a technical standpoint, it's quite possible. Whether it's approved is another story. I've seen install manuals that say daisy-chaining a serial connection is OK but haven't seen it for Gillham. Hopefully Ryan or Jesse will be along shortly to weigh in.
 
The 155xl uses gray code. The ES can use either gray code or RS232.


c177tx said:
new GPS 175 for 4095 and a used ki209 picked one up for 300 bucks. The install cost will be the same as your old tech. the 175 will not need annunciator if located in the pilots angle of view.

https://avionics-laf.com

find the 175 and put it in the cart to see sales price. They ship free to texas and no sales tax. I purchased a GTR225 from them
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So..free shipping and no tax ? Wow !
 
Okay, there is a small Mid Continent indicator that has MSG and WPT indicators. It appears that these are used with the 300 and 155 units and serve as the required annunciator. In particular it is the MD40-242L. Does this sound right?

Also, the MD40 is a 2 1/4” instrument. Is this instrument allowed in a certified aircraft or is it only supposed to be used in an experimental?
 
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asicer said:
From a technical standpoint, it's quite possible. Whether it's approved is another story. I've seen install manuals that say daisy-chaining a serial connection is OK but haven't seen it for Gillham. Hopefully Ryan or Jesse will be along shortly to weigh in.
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Sure, you can splice parallel altitude encoder output as well. Just a lot more splices! Both the 155XL and ESG can take parallel or serial altitude data.

However, I still really caution going with a new install of something like the 155XL. It’s ~24 years old, never had a large install base and who knows how long data subscriptions will still be available.

Also, if you are planning on flying IFR with it, these are before the AML STC days with manufacturer provided AFMSs and pre-approved data for 337 … you are going to have to write an AFMS for the unit and get it approved as part of your field approval to do an IFR approved install.
 
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I appreciate your feedback Ryan. I got a really clean 155xl with an indicator, annunciator, data card, programmer, connectors et al for a really good price. Not sure if I will use it. I still might save up for a 175, but it’s really tough to justify a 175 for this airplane.
 
I totally understand. Just trying to make sure you are going in eyes wide open for the install, much easier process with a pre-approved AFMS and an STC! Not to mention would hate to see you put it in, do all the paperwork and then have Jepp end db support and have spent all the time and money to put it in. If you are doing it as a supervised install or otherwise getting the install inexpensively I could see doing it.
 
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