The International Cessna^® 170 Association

My plane has a remote compass that does not appear to be properly documented. The transmitter is located in the fuselage (7.5lbs, arm 148", moment 1110), the indicator is in the instrument panel, and there is a 14V to 26V 400hz inverter located on the firewall. The only reference to this compass is a 1972 logbook entry stating that it was installed. There is no 337 or STC in my records nor in the FAA records that reflect the installation. The work was done at the same time that an AVCON O-360 conversion was being installed but I don't have the AVCON drawings or installation instrtuctions so I can't tell if it was a part of that conversion or if it was just done at the same time. Does anyone have any information or knowledge of this setup?

Well thanks to a collective of members there exists a library of installation instructions for various 0360 STCs that I can get my hands on. I have not reviewed each document but feel certain that a remote compass would not be part of any engine installation instructions. I'll bet those familiar with the instruction will chime in here and confirm my suspicion.

You say there is a log entry. Is this log entry a different one than the engine installation? Do you have a 337 for the engine install and could it be included on that?

I would inspect the various parts and try to come up with the manufacturer which would help tracking down the system you have. That would then lead to information as to the possibilities that the installation could have been done with. Either a one time approval or by STC.

I think that this thing is a Remote Flux-Gate compass. There doesn't seem to be much information about them oline . I haven't squeezed down the fuselage yet to look for data that may be stamped on it because of the Aux Fuel Tank. Hopefully a picture is worth a thousand words.

No help on the compass but I thought those aux tanks sat on the floor? I've never actually seen and installation inside.

Is there a slave/unslave switch on the panel some where?

The Aux Fuel Tank is a 22 gal Fairchild PT-19 wing tank. It was installed at the same time as the AVCON conversion in 1972. The aux tank installation is documented (337, drawings, WT/BAL, C.G. calcs, AAFM, placards) and field approved. The remote compass seems to have been overlooked as far as installation paperwork goes.

Robert Eilers wrote:Is there a slave/unslave switch on the panel some where?

No slave/unslave switch. There is a power on/off switch for the inverter. The output of the inverter goes to the indicator on the panel, and a shielded cable goes from the indicator to the black box in the fuselage.

This probably makes no difference to the discussion, but this instrument looks like a slaved RMI to me. Is it?

John

jrenwick wrote:This probably makes no difference to the discussion, but this instrument looks like a slaved RMI to me. Is it?

John

The compass is fixed...no rotation. The needle shows your heading. The other pointer is adjustable via the front knob...adjust it to the desired heading. Keep the needles lined up and you're on heading. The only connections to it are from the inverter and from the black box in the fuselage.

Wow, that's different! Thanks for clearing that up...

John

As long as the compass system is in addition to a magnetic compass (doesn't replace original equipment), and as long as it is approved for aircraft, it needs no further approval basis than a logbook entry attesting to installation meeting approved methods/materials, and wt/bal. It is auxilliary equipment.
Just because a piece of equipment is installed in a Cessna 170 (or anything else) which perhaps doesn't ordinarily have such equipment.... doesn't mean it's illegal to install, nor does it mean it needs any special approval basis. If it's aircraft-quality stuff....and if it's installed properly and documented... it doesn't need a 337 unless the installation altered the aircraft in some major way.
That looks like a simple, good installation, and it certainly is aircraft equipment. Enjoy it.

(Now, that "field approved" fuel tank is another matter.....)

The compass works fine so I won't worry about that anymore. I'll crawl back there some day and see if I can figure out exactly what it is.

Ok, George...I'll bite. Should I start worrying about my Aux Fuel Tank?

Bpaige, fuel tanks, especially fuselage-mounted tanks, must be ventilated...not simply vented. In other words... in the event of a leak in the seams of that tank or any of it's fittings... where will the fuel and vapors go? In the original "Javelin" tanks approved for fuselage mounting in this airplane, it sat on the bottom of the fuselage and had a flapper-vent beneath the floor such that a compromised tank would spill it's fuel and vents overboard. If you think about it, so are the ones mounted in the wings. They are mounted upon a "floor" (lower wing structure) and any leaks will spill overboard into the flap-wells and root areas and into the slipstream.

The tank installation in your rear fuselage does not appear to be mounted upon supporting structure but is instead "suspended". In the event of a hard-landing that tank might break loose and collapse downward, spilling fuel throughout the fuselage. Additionally, any leaks will allow fuel and vapors to descend to the cabin floor and flow forward towards the cabin and it's occupants and equipment. It does not appear to be ventilated overboard.

The final decision as to the safety of the installation rests with the owner, regardless of any "approvals" issued by installers and other authorities. It's only my opinion, but I wouldn't want that particular installation.

bpaige wrote:

jrenwick wrote:This probably makes no difference to the discussion, but this instrument looks like a slaved RMI to me. Is it?

John

The compass is fixed...no rotation. The needle points in the direction of travel. The other pointer is adjustable via the front knob...adjust it to point in the desired direction of travel. Keep the needles lined up and you're on course. The only connections to it are from the inverter and from the black box in the fuselage.

bpauge did you mean to say you are on heading, instead of on course?

Where is the Blue Leader to explain this instrument.

johneeb wrote:bpauge did you mean to say you are on heading, instead of on course?

Good point, John. It shows the plane's heading relative to magnetic north. Thanks for the correction.