View Full Version : Instrument panel modifications

09-23-2006, 11:30 PM
I am flying a 1955 PA-22-150. I would like to modify my instrument panel to allow the transponder to sit on top of the panel on the right side. I have seen pictures of some panels that have had the contour on top of the right side levelled out, allowing for avionics to be placed there. If anyone here has done that mod, I would appreciate any info/suggestions/copies of 337's to facilitate this. Thanks!

09-24-2006, 02:00 AM
Attached are some pics of the panel I'm installing in my Pacer; maybe this will help. I designed the panel in CAD and had it cut with a waterjet. I flush riveted an angle on the back of the panel after shrinking it to fit the outer contour. I did the same with the instrument panel cover, I bent it slightly and used the shrinker to get it tight against the angle flange of the panel.

09-24-2006, 02:01 AM
Attached are a couple more pics of the upper panel cover.

09-24-2006, 09:11 PM
That insturment panel is beautiful. I would like to do something like that with my other project. Did you have to make a 337 for the panel mod or just make it? I have heard many different opinions on that.

Homer Landreth
09-25-2006, 08:23 AM
I noodled the placement of a transponder there and rejected it because of the difficulty in reading the selected code and the switch positions. Up on top, if you make the mounting perpendicular to the panel, your numbers and switch labels are in that same plane of view so when you look over at it , you can see about the first two settings and you have to move your head over to the right to see the rest of them. If you angle the mounting to point the numbers into your line of sight, the mounting looks "unorthodox". Since a transponder setting is not changed that often during flight, I opted to mount it beneath the panel on the right side and I framed it in along with a DME 890, and angled them over into the field of view of someone looking at it from the pilot seat. I like it and the ratio of people seeing it and liking it is about 80% like it and 20% don't like it (but they led depraved lives as children). Just another comment as a "heads up" though, be sure that you know the exact depth of the units you are trying to get into the center stack area, because when you get within about 4 to 5 inches from the bottom of the center stack, you start to run into conflict with the confluence of the structure braces going back into the web that they form right in the center area. You can see a good view of that in the photos taildraggerpilot posted. My stack is a CP136 Audio panel, two MK-12D and a KLN89B GPS. The GPS is a bit over 4 inches shorter than the MK-12D and it barely fits length wise into the panel at the bottom because of the support tubes. The second MK-12D has it's back tilted up ever so slightly to get it clearance over the support braces. In my next lifeform when I come back as Bill Gates, I will buy two KX125 navcoms and use external indicators and that will occupy less than half the space the two MK-12D take up, and will get it all into the center stack with room to spare. As far as a 337 is concerned, I would expect to need one. FAR43 has this to say to define a major modification; (xii) "Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, deicing or exhaust system. When you are adding and moving circuit breakers and DC Bus wiring around to accomodate the new panel locations I think it could be easily stated that you modified the basic electrical system design. I would suggest not doing a whole lot of cutting and riveting etc. for a new panel until getting the Data Approval phase of a field approval completed. Get your plans drawn out and schematics and parts identified and get it signed off by the FSDO, and you will take the risk of disapproval at a later inspection out of the picture. Good Luck.

09-25-2006, 06:43 PM
I agree with Homer in that modifying the basic electrical system is a major alteration, i.e. installing a radio and subsequent circuit breaker. However, I feel that modifying the panel is a minor alteration and only requires a log book entry. The reason being the instrument panel in the PA22 is non structural and is attached to the boot cowl with non structural fasteners (sheet metal screws with tinnerman nuts). Similarly, the stock panel is also supported via the throttle cable, mixture, primer, and other associated items. The panel essentially can be a remove and replace item. AC43.13 says it's acceptable to organize the instrument panel (gyros) to the basic "T" configuration.

The 337 for installing the electrical component (radio) should automatically include the circuit breaker and relevant data like a load analysis and when approved permit you to install the circuit breaker where applicable in the panel. I guess I see it both ways.

09-26-2006, 03:12 AM
Thanks all for the info. Homer, your point on the equipment depth is well taken. I have a Garmin AVD 100 to go in at the bottom of my panel, because on my model the brake cable passes right through the center of the radio stack. Kinda makes it hard to put much in there. That is why I need to relocate either the comm 2 or the transponder. My logic is to keep the radios together, and since they are more likely to receive inflight attention, closer to the pilot. I also see the point on getting the data approval and field approval before doing any work. Hopefully I can find some paperwork from someone who has gone there before me to facilitate things on my end. I am but a student and new owner trying to find my way in this new and strangly confusing world ;-) I currently have a Narco comm 11b. I had a Narco nav 12, but it took a powder on me, so I wish to install a King 170b as my Nav 1/Comm 1 and the garmin for nav 2. I gotta do something soon, cause my checkride is coming up, and I believe that I have to have a functioning nav radio to take the ride in my plane!

Homer Landreth
09-26-2006, 08:29 AM
Hello. A couple of other things. Your admission to being a student and new owner yields to the admonition that you cannot install the equipment or modify the plane unless you are an A/P or working under the supervision of an A/P or A/I who will ultimately sign off the installations. Additionally, be careful about a KX-170B radio. Most of them that are available on the open market are some pretty tired old radios and are probably available because the owner doesn't want them in their plane. The KX-170 B tuning on the Comm and Nav side is done with wafer switches that, with age, become intermittent and sometimes just plane broken. The switches are financially prohibitive to replace, and if you get a KX-170B with a bum switch, you can't even use it as a good boat anchor. In view of your space limitation, you might want to take a look at some of the digital low profile comm only units, and just go with a single comm and your AVD 100 GPS. (Contrary to popular belief, unless you are flying into special category airspace, you do not need to have a VHF Nav in an airplane for a private pilot flight check. The pratical test standard requires only the demonstration of the use of an airborne navigation system. Which a GPS is) Finally, don't do a whole lot of waiting for someone else to cough up a 337 for you. Your 337 submittal (if needed) is a description of what you did to your plane, and what someone else did to his does not always wash over to yours. Good Luck

Tom T.
09-26-2006, 08:50 AM
So Homer, all these years we all been thinking you needed a VOR for our flight tests, is not true? We been discussing all this in our hanger flying, and if that is the case, it will simplify a few problems for some friends of mine.
Tom T.

09-26-2006, 10:03 AM
Make sure any radio that you put in the aircraft is 720 channel. You can run the 360 channel radios but you can not install any anymore. I agree with Homer also, maybe look for a newer slimmer radio. I do not recommend running around with out a radio though. I am a CFI and the FAA and I stress that the air up there is getting busier by the day and it is really an important safety factor to have a radio. But you can find a slim digital radio for less than a thousand bucks, but have someone certified install it. A simple radio would not cost much to have installed.

As for the Navigation portion, you do need some form of built in navigation. You notice I said built in. All the examiners from the Minneapolis area have told me that means something that is panel mounted permenantly. Like a panel mount gps, adf vor and so on. I think in some cases you could sway them with a handheld but I would not recommend it for a checkride.

09-26-2006, 10:09 AM
I do not agree with the installation of a radio being a major alteration. I think by electical system they mean like going from an generator to an alternator. I have am an A&P and have assisted in intercom installations, GPS and radio installations in my own aircraft and none of them has needed a 337. You only need a 337 and a flight manual supplement for an IFR CERTIFIED GPS. I was working with a prominent and certified repair station for Avionics in the Minneapolis area. Something as simple as the above is not really changing "electical system". I read the system as the charging system (ie: battery, gen/alternator, battery cables, ect.)

As for the panel, now that I look at it that way it really is not held by anything structural, which would mean it is not itself. Thanks Ben for that point of view.

Homer Landreth
09-26-2006, 10:15 AM
It is true. You have to walk through FAR 61 which says that your plane has to be capable of performing the required operations and that points you to the practical test standards which lists "airborne navigation system". It says nothing about VHF or anything else. Think of it this way, For a private pilot check ride, you don't have to demonstrate the use of a glideslope if you don't have one, or an ADF either. The same goes for a VOR, if you don't have one, and you do have a GPS, that is your "airborne navigation system". However I am in reference to the private pilot check ride, obviously the "required equipment" for an instrument check ride or any other advanced rating would be different. The other issue is that if you have to go into a Class B or TRSA area which is defined in reference to VOR radials, then you would have to have and demonstrate the use of a VHF Navigation system. The long and short of it is if you are based out of a small airport in the middle of anywhere, and you are flying for a flight check to some other airport and bypassing special use airspace a GPS would be all you need to demonstrate the requirement, and for the rest of your flying career, you may never have the occasion to use a VOR. (I am saying GPS, however a LORAN, or ADF would also suffice as an "airborne navigation system".)

09-26-2006, 10:29 AM
Homer, unfortunately all is not consistent with the FAA. I am presently discussing an intercom install and they are agreeable to a field approval BUT the intercom has to have been TSO'd. Since it is, I am not sure what would have happened if it were not. This same FSDO requires a 337 field approval to add a placard (aircraft limitation) indicating that a GPS installed for VFR only is "not for IFR use". I do agree with all you say, but it is really up to the PMI you are stuck with.

Tom T.
09-26-2006, 10:38 AM
Would my 2000 Lowrance mounted {on, not in} the instrument panel work for my friend to use for his check ride? He can use the vor nav in it for any vor work!
Tom T.

Glen Geller
09-26-2006, 12:38 PM
Micheal, I have a 55 PA22 with the I presume original low panel. The radio stack is on the left side, with only the fuel gauge and tank select switch along the very left edge. The xponder is on top, with a MX170 Nav-com below. A portable 2x2 intercom vecro'd to the floor just left of the flap handle. Works very well.
There's an ADF mounted below panel where my knees like to be, I may yank it some day but I like to listen to Air America Radio in flight!
I also carry a Sporty's handheld nav-com in case of electrical failure.
I'll try to take some pix in a few days and post them.

09-26-2006, 12:54 PM
I don't know if it is relevant anymore, but 15 years ago I took a checkride in a Champ with nothing but airspeed, altimeter, compass and a Comm radio. The examiner let me use a simulator to demonstrate instrument proficiency. I don't remember whether I did VOR navigation on the simulator or not.

Homer Landreth
09-27-2006, 07:06 AM
Unfortunately the concept of "agreeing" or "disagreeing" is not the correct adjective to apply to this subject, however it always seems to creep into the discussion, a more appropriate term is "complying". As Andy has pointed out in his response, we are at the behest of the FSDO we are working with. I have never been really reluctant to do a 337 for anything where there is a potential for a later determination that a Major modification has ocurred. I have never been criticized for submitting a "needless" 337. Filling out the paperwork is not that big of a deal, especially for an avionics component that has an installation manual produced by the manufacturer.

Homer Landreth
09-27-2006, 08:11 AM
If you are saying that the only navigation system available is the Lowrance 2000, the answer would be no.

Here it is direct from FAA Order 8400.1.


A. Portable Units. Portable GPS receivers can only be
used as a supplemental aid to VFR in conjunction with an
approved primary means of navigation.

Tom T.
09-27-2006, 08:41 AM
Thank you Homer, that pretty well says it. I have 2 friends that just have a com radio only and they are about ready for their check ride.
Tom T.

10-03-2006, 02:06 PM
I spent a little time with Ken Ellis at his restoration facility in Warm Springs, GA last month as part of a chapter visit. He showed me an STC'd modification to the tubing that interferes with the radio unit depth in the lower portion of a center stack (as Homer referred to earlier in this thread). It requires some tube cutting and welding but the finished look is very satisfactory. Ken does this STC on all his PA-22 restorations. He does not own the STC but knows where to purchase it. He is a SWPC news advertiser "Ragwing Renaissance", and very knowlegeable regarding upgrades and STCs.

Reid Murphy
PA-22/20, N9999A
Falcon Field GA, FFC

10-03-2006, 11:36 PM
Again, thanks all, for the info. I haven't decided what the final outcome will be. You have given me a quick and dirty fix, though. I can put the GPS in the bottom of the panel where it is short enough to use the space, and as it has a King CDI to slave to it, pull the bad Narco Nav12 and be able to use my ac for the checkride. I have a pretty good A&P who is willing to work with me in getting stuff installed. I am just trying to dig up example paperwork to make it easier on the both of us. As to the King radio, I already have a 170b in working order, so it will be the one that goes in, at least for a while. Michael

10-09-2006, 05:33 PM
I do not agree with the installation of a radio being a major alteration. I think by electical system they mean like going from an generator to an alternator. I have am an A&P and have assisted in intercom installations, GPS and radio installations in my own aircraft and none of them has needed a 337.

================================================== ========

I'll chime in here with my 2 cents ! :D

for starters any equipment installed in the aircraft that is NOT in the TCDS requires either an STC or a Field approval no matter how simple it is ,and both of those documents must be closed out by an IA.
If you installed a radiio or GPS that is NOT specifically listed in the TCDS and did not document the alteration on a form 337 then the installation is NOT approved and the aircraft is NOT airworthy !
READ (and uderstand) your FARS !!!!!!!

Jerry Russell
A&P, IA :)

10-09-2006, 08:23 PM
I have to agree with Jerry on this one. I just installed an intercom and the inspector wanted to make sure it was TSO's else he was not going to be easy on a field approval for install. Maybe some FSDO's are easy but I still agree with Jerry

Homer Landreth
10-09-2006, 11:25 PM
I have read your response here several times and can not convince myself that it is anything but derogatory and insulting. First off, anyone doing maintenance under a license, is slaved to FAR part 43 whether he is considered to be, as you put it, "eeking out a living" or not. Do you consider yourself not "eeking out a living" and as such have a different set of requirements that you are allowed to comply with ? Your term appears to be somewhat disrespectful to the many people who are in fact "eeking out a living" maintaining airplanes. Additionally, you seem to be indicating that there is a stigma attached to attending IA seminars that makes the attendee be in a category of IA that is different than an IA who does not attend them. In your eyes, does attending IA seminars reflect negatively on an IA? Also, I am mildly interested in hearing your explanation as to where on a 337 the reference to "Tribal Knowledge" is made when signing off the return to service. Finally, just out of curiosity, who specifically are you referencing when you say; the last guy who heavily thumped Title 14 of the CFR's with his fingers didn't fare well on this site, and what specificially was the reason he was percieved to have "not fared well" ?

10-09-2006, 11:57 PM
My wife and son earned their private pilot license in 2005 both of them were required by the FAA to show knowledge of the use of the VOR in flight, we borrowed a friends 150 with a VOR and used both planes in the flight tests.

Homer Landreth
10-10-2006, 12:56 AM
Hi John;
I was thinking of you the other day, we opened the last bottle of Mt Palomar Syrah, and the level of Bistro Red and Cabernet reached the danger level low so we need to plan a trip out to Temecula pretty soon for a restocking. Anyway, I absolutely knew that somewhere out in aviation land would be someone who had to produce a VOR equipped airplane for a flight test by order of the Designated Examiner. I am surprised there have not been more replys relating they had to do that. Maybe it is because there are probably not too many airplanes that don't have a VOR. Anyway, per the practical test guide you did not have to do go get a VOR equipped plane. However, as is the case in a lot of maintenance issues such as those discussed in this thread, the FAA has a lot of different people, Maintenance Inspectors as well as Designated Flight Examiners, who interpret things differently, and if they have what you want, in your case the pilots license, then their interpretation of the rules gives them 51 percent of the votes. Obviously you had little latitude for argument, and could have gotten into the situation where you win the battle but lose the war. Anyway, I stand by my interpretation of the chain of references and feel that they unequivacly support that you only have to demonstrate the ability to use an "airborne navigation system". If you come with a VOR equipped plane and it also has a GPS, the examiner can require you to demonstrate the use of both, and can actually require you to demonstrate the ability to use all equipment on board the plane, but there is no regulation or pratical test standard that requires you to furnish a VOR equipped plane for the flight test.

10-10-2006, 09:57 AM
I used to run a part 141 helicopter flight school - many years ago. At the time, I tried to convince the local GADO (remember them?) that the pilot, the compass, and a sectional could be considered an "airborne navigation system". Needless to say, I had to install a couple of VORs in our aircraft for the flight checks. :D

Homer Landreth
10-10-2006, 12:03 PM
No problem, thanks for the clarification, the original post just came through my mind on the sinister side. :o

Steve Pierce
10-11-2006, 07:46 AM
So are you saying if I replace a radio with a different one I have to file a 337 form?

Homer Landreth
10-11-2006, 08:36 AM
:mad: I think we out to declare a prohibition on any more "do you need a 337 for radio's" questions. After all is said and done and for the gazillionith time, those who say "no" remain of the belief that you don't need one and those who say "yes" remain of the belief that you do. My final input is this: I just recently got United States airworthiness certification for a PA-22 that was U.S. registered and then relocated to South America for a few years and returned. Before he would grant U.S. airworthiness, the DAR made me accomplish a 337 for every piece of electronic equipment and radio that was not on the TCDS. So do with that what you wish, and associate it with your personal belief that (as many have found out), doesn't mean a hoot when the FAA is standing there wanting a 337 for a radio installation.

Glen Geller
10-11-2006, 07:51 PM
Homer, you should fly up here to Oregon sometime, we have the best Pinot Noirs this side of Bordeaux! (There, that changed the subject!)

Homer Landreth
10-11-2006, 09:58 PM
I could do that Glen, thanks for the tip. Years ago I used to fly a Cessna 340 into Klamath Falls a couple of times a week. I liked the scenery even though they told me there haven't been "falls" in Klamath Falls for about 100 years. Also, I used to go to a place that the name escapes me now, but they were famous for having a Shakespere Festival yearly.

Stephen 998
10-12-2006, 12:12 AM
Ashland, Oregon

Homer Landreth
10-13-2006, 10:23 PM
That is it ! Thanks ! Romeo - - Romeo - - Wherefore art thou . . .Never mind. ;)

05-13-2007, 11:15 AM
I just wanted to post some pictures of the panel. It's not finished yet; I still need to add the placards, but it's close enough to post some pictures. The radios are wired with Approach Systems Hub and Cables and the Instruments are lighted using Superior Panel Technology fiber optic lighting. The wiring is still in progress, so please excuse the bundle of spaghetti.

Homer Landreth
05-13-2007, 12:33 PM
Hello Ben; You are obviously doing a great job by yourself, but in the spirit of this forum I wanted to offer a couple of suggestions. One, are you planning to have an avionics cooling fan ? The center stack looks real tight for circulation and heat dissipation. It appears to be a ripe circumstance for heat "soakback". There are a bunch of three and four port cooling fans that are relatively inexpensive and don't occupy much space and have a respectable CFM output that would help in heat dissipation. Also, do you plan to have an analog or rectilinear NAV CDI instrument? I have an IFR cerified KLN 89B GPS in my plane, and by law you have to have a separate CDI for IFR approaches, but by having it I have concluded that I would not really like to rely on a panel mounted radio's digital CDI for even non approach really close tolerance navigation. Maybe it is a lot of years and a lot of hours seeing needles swinging back and forth, but I get a lot of input from needle activity that I use for decisions, and I have not yet reached that level of comfort with the LEDs imagery just turning off and on.(Plus I design them, and know their limitations and nuances) Anyway, I have found that even when not on an approach, that I use the rectilinear CDI and not the panel digital display. Soooo . . just some input for thought. (My associate over at Bombardier has been telling me about your nasty weather of late, I don't miss that kind of weather at all :eek: , keep your head down and keep your plane inside.) Best Regards Homer.

05-13-2007, 02:10 PM

Thanks, but I do have to give a great bit of thanks for my friend, and IA, who has done a major portion of the work on this old bird. He is allowing me to work my project under his supervision so I can work toward obtaining my A&P. It's crazy, working in the aviaiton business as an engineer, I can design aircraft parts, but I can't maintain the parts I desing without an A&P.

I do have a cooling fan and it goes on the shelf where the pliers are in the last picture. The fan I have is called the "Ice Box" made by Troll Avionics. It's a three port fan and really blows the air. I am in the process of installing it, but still need access to the master and avionics bus.

As for the CDI, I'm not planning on installing one at this time. The radios am installing are a Garmin GNC250XL and a Garmin GNC250. I didn't want to spend the extra money upgrading to IFR due to the recurring cost of keeping things updated.

The weather around here has been severe, but this weekend has bee a nice one.

10-03-2007, 09:33 PM
I believe you can install any transmitter that meets the FCC rules 720 or not. The regulation has to do with the stability of the frequency not the number of channels. Acceptable radios are listed somewhere and inclide (or used to ) the 360 ARC synthesized radios among others. I could be wrong, but I used to not be. (as is often the case)