If you were to lose radio contact six hours into the flight enroute
from Sydney to L.A., would you continue to L.A. or turn around and
head for Fiji, or something else entirely?  And, if your answer is
"turn around," would you announce this to the passengers or keep it to
yourself?

Actioncat --

Since you seem to be satisfied with the answers, I'll post an
"official" one so that this can be closed!

Though Athena4-GA may not be an airline pilot, they've given you an
excellent answer.  In these days of heightened security, you might
also expect a fighter escort upon arrival.  But I digress.

The lost communications procedures used by the airlines and
international air traffic control follow those of the FAA in Airman's
Information Manual, Section 4, "Two-Way Radio Communications Failure."
 The pilot is to continue on the route assigned or the flight plan. 
They are also to set their transponder to a code of 7600, which is
used to highlight a radio failure.

Of course, were there an emergency, the pilot is given a wide range of
discretion for flying to the safest location.

You may be interested in the Atlantic Flight Guide published by the
FAA and its comments on two-way radio failure (p. 20):
FAA
"North Atlantic International General Aviation Operations Manual" (2004)
http://www.faa.gov/ats/aat/IFIM/natsmanual.doc

A good Google search strategy to search the AIM and rules is:
"Airman's Information Manual" two-way radio communications failure

Best regards,

Omnivorous-GA

The answer was helpful, it was easy to understand, it was friendly,
and as a bonus I got some helpful links to supplemental material.  And
I also appreciated those who answered "for free," that was very nice
of them.

You would certainly need to inform the passengers, though you might
just mention a minor technical problem.

Let me rephrase: You would certainly need to inform the passengers,
though you might
just mention that is is due to an unspecified minor technical problem.

I am not an airline pilot.

There is no need to turn around or choose an alternate airport for
lost communications - there are already accepted/established
procedures for lost communications (for oceanic routes, ICAO documents
describe these).  So the answer is "continue to LAX).

The passengers don't need to be concerned, but the pilots, at their
discretion, may make an announcement of this fact.  (If turned around
or alternate airport is chosen for other reasons, pilots would make an
announcement).

Note also lost com is very unlikely as oceanic aircraft normally have
2 HF radios for long range communications and also Satcom (so the
pilot can use the telephone through the satellite link).  There are in
addition 3 VHF radios the pilots can use to communicate to nearby
aircraft (if within range of about 200 miles) to relay information to
ATC.  Modern aircraft also have controller pilot data link
communications (CPDLC) and automatic dependent surveillance (ADS) to
report the aircraft's position to ATC on a data link (not voice)
automatically.  If all of them fail, the established procedures (ICAO)
take over.

Actioncat --

Though Athena4-GA may not be an airline pilot, they've given you an
excellent answer.  In these days of heightened security, you might
also expect a fighter escort upon arrival.  But I digress.

The lost communications procedures used by the airlines and
international air traffic control follow those of the FAA in Airman's
Information Manual, Section 4, "Two-Way Radio Communications Failure."
 The pilot is to continue on the route assigned or the flight plan. 
They are also to set their transponder to a code of 7600, which is
used to highlight a radio failure.

Of course, were there an emergency, the pilot is given a wide range of
discretion for flying to the safest location.

You may be interested in the Atlantic Flight Guide published by the
FAA and its comments on two-way radio failure (p. 20):
FAA
"North Atlantic International General Aviation Operations Manual" (2004)
http://www.faa.gov/ats/aat/IFIM/natsmanual.doc

A good Google search strategy to search the AIM and rules is:
"Airman's Information Manual" two-way radio communications failure

Best regards,

Omnivorous-GA

It sounds to me as if this question is describing one of the plot
elements of the ABC television series "Lost."

Indeed it is, pinkfreud -- it was driving me nuts, and I don't know
any pilots to ask.

Thank you ALL for your comments, I appreciate it very much! I'm not
sure how this question deal works but I would have been happy to pay
for any one of the answers, if it's not answered "officially."  You've
been very helpful, thank you for taking the time!

Thank you for the compliments, omnivorous-ga.

I didn't know it was a plot of a TV series, pinkfreud-ga! (Of course,
then all bets are off and you'd have to accept their version of
events, which may or may not have to do with reality).

Lost communication procedures have been established for a long time -
and the US domestic rules are prescribed by the FAA and the Oceanic
rules are as per ICAO (International Civil Aviation Organization) and
are usually accepted as is (Member countries can modify them if
required and publish them).

An additional tidbit is that on the north atlantic tracks, you can
almost always find another airplane (a few) within VHF range as there
is a lot of airline traffic.  In the Pacific, it is somewhat less
probable.

[athena4-ga happens to be a him (and happens to be helping create an
oceanic "passing" procedure at the moment)].

Athena4 --

Have you ever met Margrit Waltz, the well-known ferry pilot?

A link for you:
http://www.aviating.com/mooney/past/progr4.htm

Best regards,

Omnivorous-GA

Omnivorous - no, but thanks for the webpage.  Sounds like an
interesting occupation!  I have never done ocean crossing in a general
aviation airplane.

Best Regards.