Thank you. I have finally torqued enough people off to make this a legitimate discussion. Salty, I apologize for getting on my high horse, but this discussion was headed for a graveyard spiral and I really thought it needed a kick into the light of day. Bell206, you are a light in the midst of darkness. Thank you for your well-thought out discussion. Those whom I criticized for English errors, forgive an old professor to whom it is important to convey correct writing in the language of the land. To all, let's bring this down to a conversation.
STC. Supplemental Type Certificate. Supplemental is the operative word. Attached (I hope, with the limited way of attaching files on this board) is the Type Certificate Data Sheet for my particular airplane, the blue-on-blue 1958 Cessna 182A. I could do the same for your aircraft, but let's just use this one for explanation. To change ANY item on this TCDS requires a STC. I defy anybody to find on my TCDS anything that requires an airspeed of any particular type, design, accuracy, or approval. The STC has become the unintended but convenient way of getting some sort of non-required "approval" for "stuff" we want to put on the airplane. I want to put an inspection plate on the airplane that came made out of 4041 aluminum with 5052 alloy. Did that number appear anywhere on the TCDS? No. Is that a major change to the airframe? That's MY call as the airframe mechanic. Does it require a 337 form? That's MY call as the mechanic, and I say No and No to the prior two questions. Am I on the hook if one of those inspection plates cracks, breaks off of the wing, jams in the elevator mechanisms, and causes a smoking hole in the ground? Yup. That's what it means when you get that little piece of paper that says, "The Administrator, placing great faith in the judgment of ..." grants you your A&P certificate, and in even larger typeface when you get the IA.
337. The most misunderstood document in aviation. Read the title. "MAJOR Repair or MAJOR Modification" (emphasis author). And several FAA documents go on to explain what MAJOR and MINOR mean. The most important phrase in all of the explanations is the differentiation between MAJOR and MINOR. In ALL documents, there are examples given, but the most important one of all is that it is the INSTALLING MECHANIC'S OPINION as to Major and Minor. OPINION. That's why it takes us longer than getting a college Master's degree to get an A&P. Forming that opinion and making a decision. Are A&Ps infallible in that opinion? So far as I am aware, only one human being claims infallibility and I doubt he knows the difference between a rivet and a sheet metal screw. But we try. Now, I'm sure you think that 337s go to the local FSDO where they are pored over with a fine tooth comb to find any possible breach of good practice. Guess again. We send them directly to the Records Branch in Oklahoma City that files them without any scrutiny whatsoever into your microfilmed/scanned file and there they will rest for all eternity until and unless they are uncovered to prove or disprove some sort of incident or accident for your aircraft.
Now, the question becomes. Would I install a G5 for my primary flight instrumentation in my aircraft or an aircraft I maintained. You Bet Y $ @$$ I would, and not think a thing of it. Would I do a 337? Not a chance in #e!!. Would I do a logbook entry for a minor modification and sign my name to it? Without a second thought.
How did I come by this "cowboy" maintenance mentality? In 1973, I wanted to produce avionics ... aircraft electronics on a budget. I researched the FARs and found a beauty loophole FAR 21.303 (b)(2) (recently rewritten to 21.2 or something like that). That FAR said you had to have Parts Manufacturing Approval ("PMA") to produce any part intended for use on aircraft UNLESS (and the UNLESS is the big part) you were the owner or the operator of the aircraft. I researched the genesis of the regulation and found that it was put into the regs back in the 1930s for cropdusters that dinged a wingtip and needed to replace it overnight. If cropdusters could replace wingtips, pilots could build radios. Oh, My God. They flew the Chief Maintenance Inspector and his crew out to San DIego and we had a rather incongenial meeting one morning. "You can't do that." "The hell I can't" "We'll get the General Counsel to write an opinion." "Please, go ahead."
General Counsel wrote a four page opinion that said that the FAA opened the door to this stuff in 1930, and not only is it legal, but it is permissible under these guidelines ....and three pages of guidelines followed.
Yeah, I've been interpreting FAA regulations for a **real** **long** time and I've come to the conclusion that most of them are in the minds of folks who don't have a real clue what they really say and FAA folks who are willing to promulgate that misinformation.
I may be wrong.
Jim
