Terminology of New WAAS, VNAV, LPV approach types

"Richard Kaplan" wrote in message
news:[email protected]...
There was an intresting talk at Oshkosh about the WAAS system by one of
the
members of the UPSAT engineering team.

As an aside, he defensively mentioned that the CNX-80 would be certified
for
precision approaches in "fourth quarter 2003." The sales rep on the floor
were more confident that certification would occur in October 2003. Who
knows what exactly to believe.

Perhaps more interestingly, he showed approach plates for
under-development
WAAS LPV approaches to Gaithersburg, MD and Red Wing, MN with minimums of
250 - 3/4. Those approch plates had separate minimums listed for LPV,
VNAV/LNAV, LNAV, and circling approaches. He indicated that currently the
CNX-80 can only fly an approach down to LNAV minimums but ultimately it
will
meet LPV minimums. However, when flying the LPV approach if the WAAS
system
should be flagged as inoperative then the pilot could instead fly to
VNAV/LNAV minimums.

He indicated that current-generation non-WAAS receivers are not approved
to
fly the precision VNAV/LNAV approaches yet the WAAS-approved CNX-80 will
be
approved to fly VNAV/LNAV approaches with WAAS inoperative.

The AIM is somewhat ambiguous on this topic, implying that VNAV/LNAV is
separate from the WAAS system but requires accuracy equivalent to
barometric
altimetry.

I am not sure what to make of this, and I suspect there will be an
important
learning curve when these approaches and these GPS receivers become more
common.

Any further thoughts?

This way you get something for all those WAAS development dollars.

Always go with what the engineer says over the salesperson. Sales people are
generally clueless.


"Richard Kaplan" wrote in message
news:[email protected]...
There was an intresting talk at Oshkosh about the WAAS system by one of
the
members of the UPSAT engineering team.

As an aside, he defensively mentioned that the CNX-80 would be certified
for
precision approaches in "fourth quarter 2003." The sales rep on the floor
were more confident that certification would occur in October 2003. Who
knows what exactly to believe.

"Richard Kaplan" wrote in message
news:[email protected]...
This is a follow-up to my earlier posting.

I received a follow-up email and then spoke by phone today with an FAA
employee who has been working on GPS issues for a number of years. He
clarified this to indicate that a complete WAAS failure (horizontal plus
vertical data failure) would require the pilot to switch from LPV minimums
to LNAV minimums. There is also a very rare partial failure mode of WAAS
(apparently theoretical only but nonetheless programmed into WAAS LPV
boxes)
where one might lose LPV accuracy but retain enough accuacy for LNAV/VNAV
approaches.

That is because the minimums are more dependant on the pressure altitude and
the user's baro-correction input, than on WAAS itself.

Interestingly, the LPV and LNAV/VNAV approaches will be programmed into
the
database as separate approaches, although the waypoints will be identical.
If the approach is flown as an LPV approach, then the box will stop the
approach upon receiving a WAAS failure. However, if the same approach is
flown as a VNAV/LNAV approach, then the box will continue the approach
after
a WAAS failure since the approach can still be flown to LNAV minimums.

So the question (or I should say temptation) will arise on these
approaches
whether to program the box to fly an LPV approach and thus have no
means
to revert to the LNAV-only approach, or alternatively to fly the LNAV/VNAV
approach using LPV minimums, which would not be legal but could offer the
additional backup of continuing at LNAV minimums after a WAAS failure.

It sounds like there will be a notable learning curve to all of these
approaches.

And 30 years to create them.