So, the initial purpose of this thread was to discuss whether or not one
could use a handheld GPS for IFR navigation. Lots of people have been
tossing around lots of opinions with little or no references to rules or
guidance to back them up (hardly surprising...this is usenet after all...)

Anyway, for my own personal edification and enlightenment, I went and
tracked down the official FAA Advisory Circular that specifies what
the requirements are for the use of GPS under IFR. It's entitled
"Airworthiness Approval of Navigation or Flight Management Systems
Integrating Multiple Navigation Sensors", and is FAA AC 20-130A.
It's about as exciting to read as the dictionary (again, hardly
surprising). However, the Gleim Instrument Pilot Flight Manueuvers and
Practical Test Prep guide (which is where I found the reference in the
first place) does a nice job of summarizing the requirements for use of
GPS under IFR as specified in AC 20-130A. It states:

Authorization to conduct any GPS operation under IFR requires that:
a) GPS navigation equipment used must be FAA-approved and the installation
must be done in accordance with FAA requirements
i) Approval for the use of the GPS for IFR operations, and any
limitations, will be found in the airplane's POH (also called
the FAA-approved Airplane Flight Manual) and the airplane's
logbook
ii) VFR and hand-held GPS systems are not authorized for IFR
navigation, for instrument approaches, or as a principle
instrument flight references. During IFR operations, they
may be considered only an aid to situational awareness.

Aircraft using GPS navigation equipment under IFR must be equipped with an
approved and operational alternate means of navigation appropriate to the
flight.
a) Active monitoring of the alternative navigation equipment is not required
if the GPS receiver uses RAIM for integrity monitoring.
b) Active monitoring of the alternative navigation equipment is required
when the RAIM capability of the GPS equipment is lost.

This seems fairly clear to me.....

-- Dane