Hi!
If you want a simple CAD package that is easy to use and will open AutoCad drawings, this program will also do good 3d then I have the package for you.
The product is TurboCAD and a free down load is available from http://www.imsisoft.com/free/ this is an full version also the site...
If you are working on an installation that has a PT6A engine I would strongly recomend that you read this article on ESD damage to the bearings in the engine that has caused a number of in flight shut downs
http://www.casa.gov.au/avreg/aircraft/AWB/24/001.htm
I think you will find it very...
A good understanding of this is available from the powerpoint presentation available from this link
http://www1.faa.gov/fsdo/orl/files/pp/mrma.ppt
I hope that this assists
Ian