Re: Terminology of New WAAS, VNAV, LPV approach types

[Tarver Engineering]

"Richard Kaplan" > 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.

[Aloft]

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


"Richard Kaplan" > 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.

[Tarver Engineering]

"Richard Kaplan" > 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.