Bill Writes:
<<< By installing a non-TSO instrument in the aircraft the builder is "personally certifying" that the instrument is suitable to flight for the regimes of flight for which it will be used.>>>

This statement is correct but it begs the question "What does "personally certifying" and  "suitable" mean?

Bill, nor I, can point to a regulation in the FARs that says that all flight instruments must meet the applicable TSOs. This does not result in you having the freedom to call whatever you want an "Airspeed Indicator" (e.g. GPS ground speed corrected with an E6B and forecast winds aloft) because when the FAA says "Airspeed Indicator" they have a concise definition of what an "Airspeed Indicator" is, and that definition is found in the TSOs. The FARs require an "Airspeed Indicator" and "Airspeed Indicator" is defined in the TSOs. "A" implies "B" and "B" implies "C" therefore "A" implies "C" even though "A" implies "C" is not explicitly stated in the FARs.

To the FAA, "suitable" means what they have defined as "suitable" in the TSOs, therefore "personally certifying" means you have taken the personal responsibility to verify the instruments meet the applicable TSOs.

Back on 8/10 I wrote: " If you want to install an Altimeter in your airplane, and you intend for it to satisfy the altimeter part of the "Required Equipment" then to be considered an "Altimeter" it must meet the TSO for "Altimeter" because that is how the FAA defines "Altimeter". It does not matter if the altimeter was manufactured at a facility that has TSO Authorization or the altimeter has TSO Design Approval. It does not need a TSO sticker on the back (Experimental) but it still must meet the minimum functional and performance requirements specified in the TSO." I could have added "If it does not meet the applicable TSO then it is not an "Altimeter".

How do I know this? Because I have been involved with multiple certification efforts over the last decade and I know how the FAA's thinking works regarding this issue.

With freedom comes responsibility and you are free to think your definition of "airspeed indicator" trumps the FAA's definition of "airspeed indicator" (found in the TSO) but when the fit hits the shan, you WILL be responsible.

Good luck with that.

Regards
Brent Regan