Fred,
Prior to retirement I owned and operated a screen printing business that was
dedicated
to printing dials for aircraft instruments. Our customers were all the
repair shops and some manufacturers of aircraft instruments. I attended many
industry trade shows and listened to technical presentations about instruments
as well as having many friends that I consulted with while building our Europa.
>From all this I learned that an altimeter is a very complex instrument and the
performance requirements that it has to meet are very tight (look at FAR 43
Appendix
E Altimeter system test & inspection). Likewise gyro instruments (altitude
indicator and DG) also are complex and have very tight performance requirements.
What a TSO really ensures is that a quality control system is in place when an
instrument is manufactured or serviced.
So I would purchase TSO'd altimeter or gyro instrument. Pressure instruments
like
airspeeds are much less complicated and I would have no problems with a non
TSO unit.
There is a reason many repair shops will not work on non TSO'd altimeters and
gyros.
Their experience is that they cannot be repaired and depended on to continue
to meet the performance requirements. Its not worth the time nor their
reputation to attempt to work on them.
In our case, we are using GRT EFIS and EIS. We purchased the altimeter and
airspeed
option in our EIS to serve as our backup instruments. An electronic instrument
like the EIS is much more capable of meeting the performance requirements
and doing it on a consistent and long term basis.
Hope this is helpful.
Jim Butcher
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