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From: cfiaime@ihnp3.UUCP (Jeff Williams)
Newsgroups: net.aviation
Subject: Re: T S O
Message-ID: <161@ihnp3.UUCP>
Date: Sun, 29-Sep-85 22:06:34 EDT
Article-I.D.: ihnp3.161
Posted: Sun Sep 29 22:06:34 1985
Date-Received: Wed, 2-Oct-85 05:37:02 EDT
References: <130@biomed.UUCP>
Reply-To: cfiaime@ihnp3.UUCP (45261-J. Williams)
Organization: ATT Bell Labs
Lines: 52

In article <130@biomed.UUCP> lagasse@biomed.UUCP (Robert C. Lagasse) writes:
>
>      I am not a pilot but have heard of the term TSO.  I have heard of
>parts or equipment that musrt be TSO'd before it can be used in an aircraft.
>Just what is this all about?    Also, I understand that if any little nut or
>bolt breaks just about anywhere on an aircraft that it must be replaced with
>an original one from the factory or one that is aircraft approved or
>something like that.  Does this apply to all hardware on the craft?  If you
>lose a couple of dashboard screws, can't you just run down to the local
>hardware store and get a 100 pak of sheet metal screws?  How stringent are
>these requirements and who watches this stuff for violations?

TSO stands for Technical Standard Order.  A TSO applies to items 
such as seat belts, tires, radios (some), and other "standard" non-
hardware items used in an airplane.  Model specific items are produced
under a PMA, Parts Manufacturing Authorization.  Hardware in manufactured
to AN (Army/Navy) or NAS (National Aircraft Standard) specifications.

The rub on aircraft equipment is that on certified airplanes, the plane
must meet the specs shown on the Type Certificate Data Sheet, or in 
the equipment list.  This is because the only way to guarantee strength
and performance is to build each airplane as closely to the approved 
plans as possible.  Modifications can be made, and Supplimental Type
Certificates issued for the mod.

Hardware store nuts, bolts, and screws do not meet normal aircraft
standards, so can not be used for structure on an airplane.  The 
nonstructureal items such as cowls, interior, or fairings can use
non-approved hardware.  However, most A&P/AI (Airframe and Powerplant
mechanics with Aircraft Inspection Authorization) will not pass such
a machine on an annual inspection.  Fix it right, or it doesn't fly.

Experimental aircraft can use non-aircraft parts and get away with it.
As an example, when I was working for Boeing/Wichita, a friend built
a Volksplane.  His trim system pulleys were from a Smith-Corona typewriter.
The prudent homebuilder uses aircraft hardware, simply because the 
airplane is easier to get through inspection with the right hardware.

Some substitutes exist for sertain items.  All of the scarff plates
use for repairing the Funk ribs were cut from aircraft plywood purchased
at the local hobby shop.  The fairings are lattice pine rather than
aircraft spruce.  My brother rebuilt a 65 horse Franklin engine using
reworked Pinto main bearings and Briggs and Straton rings.  The original
Franklin parts are not available for love nor money.

The final arbitrator is FAR part 43, and Advisory Circular AC43-13A,
"Acceptable Methods, Techniques, and Practices - Aircraft Inspection
and Repair."

						Jeff Williams
						AT&T Bell Laboratories
						ihnp3!cfiaime


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