What's happened to the Field Approval?

[c170b53]

Why are field approvals so hard to come by? I know there are bilateral agreements that allow the regulatory agencies the FAA, CA, ESEA , MOT to standardize processes and recognize each others systems in maintaining aircraft. Has the pressure from above for a common regulatory system reached down to deprive the little guy from fixing his small machine? I have unfortunately a Avion Research instrument panel that's approved for a 172, should be a no brainer for approval in a 170,
other than the placement of the little wheel, what's the difference.

[GAHorn]

In a "nutshell" ... the past practices of "field approvals" allowed one aircraft's modification to be approved in the "field" by an FAA inspector who had inspected the modification and determined that it did not detract from the airworthiness of the airplane. A second aircraft could also be so modified, and the first approval documentation could be used by another FAA inspector as "acceptable data" to also approve the second aircraft's modification. (The first inspector had in effect, personally taken upon himself and on behalf of the FAA the liability of that modification. The second inspector, by using that previous approval as a basis, had merely placed the second aircraft's liability issues on the first inspector. Any deficiencies of the second modification rested upon the FAA with no one having provided genuine engineering support for the modification.)
The assumption was that the first inspector 1) knew what he was doing and had the necessary expertise to determine airworthiness,(something less and less likely in modern times since all the old-timers have retired) and 2) the second aircraft was modified exactly like the first aircraft. (Note: past field approvals, a type of one-time STC, had evolved into free/cheap, unsupported , undocumented, industry-wide STC's without recourse to engineering data that normally provides a certain level of surety against unairworthy aircraft.)

The problems arose when it became evident that lots of airplanes in service with field approvals purporting to be the same modification, were in fact airplanes with a myriad of differences, not only in the specific modification so-approved,...but also in lots of other ways that affected the modification (even had the actual modification indeed been exactly duplicated.)
Example: I modify my aircraft from it's 35 amp generator to a 60 amp alternator, and the inspector looks at it and issues a "field" approval. Someone else takes a copy of that 337 to his inspector who also issues a "field" approval for the second aircraft ...based upon my "field" approval for my aircraft. However, the 337 for my aircraft failed to mention that the wire gauge for my generator was also increased in size to accomodate the increased output of the alternator. Without that information the second aircraft's wire gauge was NOT increased, ...yet the second aircraft now has "field" approval for the alternator. The in-flight fire is fatal and the lawyers have a "field" day. The second aircraft owner and his family burned up in what they thought was a simple, cheap way to get an alterator in their airplane.
Furthermore, the act of "field approval", due to the end results of numerous copy-cat aircraft, had become more like an industry method of producing entire groups of aircraft which no longer met their type certificates...yet had no engineering data to support their non-compliance other than the opinion of some guy in some FAA field office somewhere. It had become similar to the childs-game of "telephone"....where one child whispers a secret in another child's ear, and then that child whispers it into another child's ear, and so on and so on....until by the time the secret makes full circle and returns to the originator it bears little or no resemblance to the original secret! In aircraft airworthiness certification circles....that is simply unacceptable.
So the central authorities have attempted to tighten up the rules and require better documentation of "field approvals"....and many of us in the "field" are no longer happy that we cannot simply alter aircraft and have it rubber-stamped "OK" like we used to. Now we must supply appropriate and proper supportive evidence that our modifications are airworthy on their own merit...rather than simply provide a bad zerox copy of an obscure and poorly documented sign-off that shows "someone else somewhere else did something similar."

(This was an attempt by me to satisfy the question asked and to provide some measure of comfort to those inconvenienced by the new policy by demonstrating a certain level of legitimacy to the FAA's new thinking. It does not signify any personal belief by me that all requests for field approvals border on "bogus" or that they might all be tantamount to making individual airplanes unsafe. While I believe the FAA is genuine in it's efforts to protect the public, I also understand that many in business hold that they are the "engine" of society and the economy, and that gov't should "prepare the field" to accept their seeds of effort to provide for the masses. This would include those businesses who have gone to considerable effort and expense to certify, "STC", and market their aircraft modifications.) My 2 cents.

[Dave Clark]

Very well put George

[170C]

Good explanation George. I'm sure a bunch of us were not clear on this issue. Thanks!

Geeze George, you shudda be a lawyer Naaw--wouldn't wish that on you!