Monday, February 20, 2006

Planning the Panel

I spent some time pondering the panel upgrade, and the difficulties associated with removing the old panel and replacing it with a new one. The panel itself is no big deal, rather it's the stuff behind it that may cause problems if I don't plan this well enough. Fo rexample, the braces that are riveted into the bulkhead behind the panel will stay as-is in order to reduce the effort, and I will work around them by placing instruments where they won't conflict with the braces. Another decision I made today is that the position of the radio, transponder, and King GPS are immutable. There is a rectangular cut-out in the bulkhead that would be difficult to move without completely replacing the bulkhead, and because the bulkhead has the front top fuselage skin rivetted to it, I'd prefer to leave it alone. I taped some approximately sized paper in the locations where the major components will (tentatively) go:

There's an obvious change here since the last iteration: the mechanical pitot/static instruments didn't make the cut. There simply isn't room for them. Still desirous of some non-powered redundancy, though, I'm planning on adding a small airspeed indicator, altimeter, and a vertical card magnetic compass in the row of three instruments between the EFIS/Engine Monitor and the radios. The gauges currently in that row will be removed as they will no longer be needed.

I haven't decided what to do with the flap switch. It's ok where it is, but I'm thinking I'd like to keep the area below the radio/xpdr/GPS stack open to allow for future growth. The clock will need to find a new home as well. The avionics master switch will get moved to wherever I decide to gather the switches. I'm thinking about a "Lighting" group of switches, and the rest of the switches (Battery/Alternator/Fuel Pump/Avionics Master) being in a separate group.

The engine controls (throttle, mixture, primer) will stay where they are.

I also did a little research into my legal basis for doing this work. The first stop was the Operating Limitations specific to my airplane. The pertinent paragraph would be this one:

After incorporating a major change as described in FAR Part 21.93, the aircraft owner is required to re-establish compliance with FAR Part 91.319(b). All operations will be conducted day VFR in a sparsely populated area. The aircraft must remain in the flight test for a minimum of 5 hours. Persons non-essential to the flight shall not be carried. The aircraft owner shall make a detailed log book entry describing the change prior to the test flight. Following satisfactory completion of the required number of flight hours in the flight test area, the pilot shall certify in the records that the aircraft has been shown to comply with FAR Part 91.319(b). Compliance with FAR Part 91.319(b) shall be recorded in the aircraft records with the following or similarly worded statement: "I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all manueuvers to be executed, has no hazardous operating characterisitics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: Vso____, Vx____, and Vy____, and the weight______, and CG location______________ at which they were obtained.

Note the usage of the words "aircraft owner" rather than "aircraft builder" or "Certified Mechanic." That seems to cover me pretty well as far as recognition on the part of the FAA that entities other than the builder (aka, holder of the Repairman's Certificate) or an A&P will perform major alterations to the airplane. But what of the referenced regulations? What, for exmaple, is "a major change as described in FAR Part 21.93?" Well, here's the applicable snippet of FAR Part 21.93:

Sec. 21.93

Classification of changes in type design.

(a) In addition to changes in type design specified in paragraph (b) of this section, changes in type design are classified as minor and major. A "minor change" is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. All other changes are "major changes" (except as provided in paragraph (b) of this section).

The part of this that is most pertinent to what I want to do is "appreciable effect on the weight, balance..." Without a doubt, I will be affecting both the weight and balance of the airplane and will have to conduct a new weight & balance inspection. Fortunately, I have been told that I will be able to use the school's scales, as long as I don't mind paying to get them calibrated.

I also have to re-establish complaince with FAR Part 91.319(b):

FAR 91.319(b)
(b) No person may operate an aircraft that has an experimental certificate outside of an area assigned by the Administrator until it is shown that--
(1) The aircraft is controllable throughout its normal range of speeds and throughout all the maneuvers to be executed; and
(2) The aircraft has no hazardous operating characteristics or design features.

In other words, I have to perform the five hours of test flying that demonstrate controllability and the lack of hazardous operating characteristics as spelled out in the Operating Limitations. That all seems eminently reasonable to me, and appears to address any questions as to my authority to perform this job.

There are a number of open questions remaining, such as whether to stay with a black panel or change to a dark gray with white lettering or a lighter gray with black loettering, whether or not to save a place for an autopilot (currently leaning towards "not"), and what to use for lettering/division lines. Here's a tricked-up panel that I like:

I like those switch guards, and I know where to find them...


  1. I say 'good call' on leaving out the old stuff. Since you are keeping with a (more or less) VFR machine, looking outside should be a pretty good substitute. I say better use the panel space for expensive avionics. Also, people are getting decent bucks for avionics on eBay.

  2. Hi Dave,

    The bird is really coming along. Seems like you are having a great time.

    Hope all is well...