From an old RAS posting by Rod Farlee:

------ Begin Quoting --------------------

TSO stands for Technical Standard Order.

The FCC specifies operational requirements for most avionics. FAA TSO
specs are environmental (temperature, humidity, vibration, shock), and
in some cases, such as IFR GPS, are operational. A TSO has nothing to
do with the manufacturing process (this is the concern of the FAA PMA,
parts manufacturing approval, process).

Try to buy a TSO'd DME, VFR GPS, GPS/COM or intercom and you'll find
there are no TSOs for these items. Also there is no requirement for
TSOs for anything used for FAR Part 91 operations except the
transponder and ELT. (altimeter, too, if you have transponder)

To install non-TSO'd equipment there is no requirement for an STC. A
377 "Major Alteration" form is needed only if the installation
requires structural modifications to the airplane or fabrication of a
mounting tray. Otherwise, it requires only a logbook entry by a radio
shop or A&P with avionics inspection authorization that the physical
installation conforms to AC 43 standard practices, and noting any
change in aircraft weight and balance.

There are some requirements for TSO'd equipment on airliners in FAR
121, but there are many exceptions (DME, entertainment, etc).

There is enough confusion among FAA FSDO inspectors over the new PMA
requirements that some of them seem to be making up there own rules in
this area, but let's not make up our own!
- Rod Farlee

------ End Quoting--------------------

Hope that this is helpful, Paul.

-John

=============

On Aug 19, 1:22 pm, "Paul Remde" wrote:
Hi,

A customer has asked me whether or not it is legal to install and use a
non-FAA-approved radio such as the XCOM 760 or FlightLine FL-760 in a type
certificated glider. XCOM's statement on the subject is copied below. Some
aircraft mechanics and avionics shops seem OK with installing those radios
and other flat refuse to. I don't have anything similar from FlightLine.

Below is an excerpt from a note received from XCOM on this subject.

"Our aircraft radio is not TSO'd but it does have the necessary FAA and
FCC approvals for fitting into certified aircraft. In fact there are
hundreds in the USA fitted to aircraft in either the standard or the primary
category." He copied me on the FAA and FCC certificates - which are on my
web site hehttp://www.cumulus-soaring.com/xcom.htm.

The customer has an A&P that is very hesitant to approve the use of those
radios - unless someone can show paperwork showing that they were received
approval to do so - such as a 337 that was submitted and approved.

I should know more about this, but I have received so many differing
opinions, that I don't know what to believe.

I imagine I'll get a million different opinions on this subject, and I
welcome them. But opinions are not what the customer needs. He needs
specific examples and paperwork - if possible.

Any help would be greatly appreciated.

Best Regards,

Paul Remde
Cumulus Soaring, Inc.