Terminology of New WAAS, VNAV, LPV approach types

"Richard Kaplan" <rkaplan@flyimc.com> wrote in message
news:0649e5cf70eaff69b32e0896c22e491f@TeraNews...
> 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" <rkaplan@flyimc.com> wrote in message
news:0649e5cf70eaff69b32e0896c22e491f@TeraNews...
> 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" <rkaplan@flyimc.com> wrote in message
news:b91eda6947d6388332cfdfafef004481@TeraNews...
> 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
> re: 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.