Date: Tue, 21 Mar 2000 20:33:48 -0600 From: "Robert L. Nuckolls, III" Subject: COZY: Re: Instruments >While Carl is correct that accuracy is good, accuracy and TSO don't >necessarily have anything to do with one another. IIRC from my Bose days, >TSO means that the device has passed a series of tests (environmental, >electrical, etc.) that mean that it's robust and meet a series of >standards. When a company makes both TSO'd and non-TSO'd parts that look >identical, the chances are good that there's no difference other than a >stack of paperwork. [As an aside, the engine I bought from Aero Sport >Power (non-certificated) is identical in every way to their certificated >engines except for the paperwork (and $2500). Same theory]. > >I believe TSO is only required if you want to sell something into the >commercial aircraft market - Bose could sell headsets non-TSO'd to general >aviation pilots, but if they wanted to sell to charter operators or >airlines, they'd have to get TSO approval. TSO is a special certification class for equipment having broad, universal applicability in many types of aircraft. For example, you find TSO test documents for altimeters, headsets, microphones, nav radios, ELTs, brakes, etc. Lots of products find their way onto type certificated aircraft via the manufacturer's original type certification (TC), supplimental type certification (STC) or field approval (Form 337) that are not TSO'd items. For example, the vast majority of products I've designed for electrical avionics systems are NOT TSO'd . . in fact the only TSO project I've ever worked was for 300A starter- generators that fit a whole bunch of different aircraft. TSO certification allows carte-blanc installability of the accessory with only attention to structural integrity of installation and proper integration with other systems . . . you don't have to re-test the product. By-in-large, TSO is of no interest to amateur built airplanes except where called out as an OPERATIONAL requirement . . . like in Part 91 we find references to TSO'd ELT's and Altitude reporting equipment. I'm not sure I searched the latest FAR91 but I think that GPS receivers for instrument flight may have to be TSO'd equipment. In part 25 the only reference I could find was to brakes. There were no references to be found in FAR23. Just because a part is "certified" doesn't mean it complies with a TSO document . . . only a small fraction of the goodies used to build airplanes are favored with the possibility of becoming TSO'd . . . the FAA produces such documents only for parts with broad applicability. Bob . . . -------------------------------------------- ( The only time you don't fail is the last ) ( time you try something, and it works. ) ( One fails forward toward success. ) ( C.F. Kettering ) -------------------------------------------- http://www.aeroelectric.com