khorton01(at)rogers.com
Guest
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 Posted: Sun Jun 11, 2006 2:37 am Post subject: Experimental IFR w/o a certified GPS or looking for a copy |
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On 11 Jun 2006, at 02:22, Deems Davis wrote:
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<deemsdavis(at)cox.net>
I recently read an article posted on Direct2. website http://
www.direct2avionics.com/pdfs/Using_GPS_for_IFR_flight.pd by a Phd
CFII that concludes that for EXPERIMENTAL aircraft, it was not
necessary for the aircraft to be equipped with a CERTIFIED GPS
receiver to legally file and fly IFR, PROVIDED that you, the pilot/
mfg can evaluate the GPS functionality, and find it provides all of
the necessary pilot input (as defined in the TSO) for IFR flight.
This sounded like it was worth looking into. I verified this
opinion with a competitor of Direct2. So off I go to study TSO-C146
the Standard document for WAAS GPS, unfortunately there is nothing
in the document regarding functional requirements other than a
reference to:
RTCA/DO-229B (which I learned has since been superceeded w/ RTCA/
DO-229C). Another Google search reveals that this document is
available but with a cost which ranged from $108-370 per copy.
Does anyone know of a 'library' where this document could be
'rented' or checked-out. a couple hundred bucks is a steep price
for someone just investigating an idea/thought.
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1. For anyone else interested in reading the referenced article, the
link is missing the letter "f" at the end. It should be <http://
www.direct2avionics.com/pdfs/Using_GPS_for_IFR_flight.pdf>.
2. The referenced article uses some fuzzy wording. They say the GPS
receiver must provide all "necessary pilot input". What does that
mean? Later on they say that the receiver must provide the required
integrity monitoring. The gist of the article seems to be that the
receiver must meet the requirements of the TSO, which is different
than saying it must be TSO'd. I.e., in theory, you could solder
together your own design GPS receiver, and legally use it, as long as
it had all the functionality and performance required by the TSO.
3. They suggest that you can purchase a non-TSO'd GPS receiver that
meets all the requirements of the TSO, and legally use it. Sounds OK
in theory, but how do you determine whether or not this receiver
meets the TSO requirements? If it really does meet the TSO
requirements, why wouldn't the manufacturer put a TSO data plate on it?
4. I've read TSO C-129 (but not the later TSOs for WAAS receivers).
There is no way you can know whether the system meets the TSO unless
you can dig into the software to look for the required functionality,
and then perform some very difficult tests to see if the
functionality actually works. You would need to provide simulated
GPS signals, with one satellite that had an error, and see if the
system was able to detect it. You would need to measure the
navigation accuracy to very tight tolerances. Etc. The required
testing would probably cost several hundred thousand dollars or more
(cost of required equipment, engineering time, flight test time,
etc). It simply isn't practical for anyone at our level to determine
whether a GPS receiver meets the TSO requirements or not.
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8
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