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GPS missed approach question



 
 
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  #1  
Old September 7th 05, 03:59 PM
xyzzy
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Default GPS missed approach question

You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require
use of the GPS to fly correctly (fly to this waypoint, then go to this
other waypoint and hold). So what do you do? Use the GPS to fly the
missed despite the RAIM failure (assuming the whole GPS hasn't gone
belly up)? Call ATC for help?

  #2  
Old September 7th 05, 04:01 PM
Steven P. McNicoll
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"xyzzy" wrote in message
...

You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require use of
the GPS to fly correctly (fly to this waypoint, then go to this other
waypoint and hold). So what do you do? Use the GPS to fly the missed
despite the RAIM failure (assuming the whole GPS hasn't gone belly up)?
Call ATC for help?


This isn't peculiar to GPS approaches. What do you do on a VOR approach
when the VOR fails and it's needed for the missed approach procedure?


  #3  
Old September 7th 05, 04:01 PM
Peter R.
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xyzzy wrote:

You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require
use of the GPS to fly correctly (fly to this waypoint, then go to this
other waypoint and hold). So what do you do? Use the GPS to fly the
missed despite the RAIM failure (assuming the whole GPS hasn't gone
belly up)? Call ATC for help


I have experienced a RAIM failure during a GPS approach, but the GPS was
still able to provide terminal resolution guidance to the missed approach
point. Another time I experienced a complete GPS failure during an
approach (BK KLN-94), but in that case I requested vectors from ATC.

--
Peter
























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  #4  
Old September 7th 05, 05:32 PM
Newps
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The GPS doesn't stop working when you get a RAIM warning. All RAIM
means is the accuracy can't be verified. I have gotten quite a few RAIM
messages on my GX55, if not for the warning you would never have known
it. The GPS hums along nicely.



xyzzy wrote:
You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require use
of the GPS to fly correctly (fly to this waypoint, then go to this other
waypoint and hold). So what do you do? Use the GPS to fly the missed
despite the RAIM failure (assuming the whole GPS hasn't gone belly up)?
Call ATC for help?

  #5  
Old September 7th 05, 10:37 PM
Scott Migaldi
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xyzzy wrote:
You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require use
of the GPS to fly correctly (fly to this waypoint, then go to this other
waypoint and hold). So what do you do? Use the GPS to fly the missed
despite the RAIM failure (assuming the whole GPS hasn't gone belly up)?
Call ATC for help?

A Raim Warning you should still have GPS and can execute the missed. I
have had a complete failure of the GPS just past the FAF and in the
soup. Approach had just told me to go to advisory. My action was to
level off, hit the switch back to approach, advise them of the situation
and request a vector, a the while holding the final approach course. I
knew I would be safe for a period of time on that course.

ATC then told me I could descend 300 more feet, the ATIS had reported
the ceiling should be 300 feet below me so I took a chance and broke out
with the center line of the runway straight ahead of me and could make a
normal landing.

Scott

--
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Scott F. Migaldi
CP-ASEL-IA
N8116B

PADI MI-150972
Join the PADI Instructor Yahoo Group
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--------------------
  #6  
Old September 8th 05, 07:13 PM
Stan Gosnell
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xyzzy wrote in :

You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require
use of the GPS to fly correctly (fly to this waypoint, then go to this
other waypoint and hold). So what do you do? Use the GPS to fly the
missed despite the RAIM failure (assuming the whole GPS hasn't gone
belly up)? Call ATC for help?


As others have said, the GPS will still work, you just won't be assured of
enough accuracy for the approach at MDA. You will still have plenty of
accuracy for holding at the MAP holding fix, though. For holding you just
need to be in the general vicinity. Also, you can continue the approach if
the RAIM warning happens after the FAF. The RAIM warning means that there
is a prediction of lower accuracy sometime in the future, probably after
you finish the approach, unless your groundspeed is very slow.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin
  #7  
Old September 8th 05, 07:59 PM
Steven P. McNicoll
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"Stan Gosnell" wrote in message
...
xyzzy wrote in :

You're supposed to go missed if you have a RAIM or GPS failure message.
But all the GPS IAP's I've seen have missed approaches that require
use of the GPS to fly correctly (fly to this waypoint, then go to this
other waypoint and hold). So what do you do? Use the GPS to fly the
missed despite the RAIM failure (assuming the whole GPS hasn't gone
belly up)? Call ATC for help?


As others have said, the GPS will still work, you just won't be assured of
enough accuracy for the approach at MDA.


So what is meant by a GPS failure message then?


  #8  
Old September 8th 05, 08:10 PM
Peter R.
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Stan Gosnell wrote:

As others have said, the GPS will still work, you just won't be assured of
enough accuracy for the approach at MDA. You will still have plenty of
accuracy for holding at the MAP holding fix, though.


I think you mean only when there is a RAIM warning does the GPS still
provide course navigation. When I experienced a GPS error message with the
KLN-94, the GPS was completely useless and needed to be recycled before it
began working again, much like a computer hard-boot.

It is also worth noting that this particular error only happened this one
time with the KLN94. Having a few hundred hours now behind a GNS430, I
have never experienced any type of GPS system error or RAIM error with the
Garmin.

--
Peter
























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  #9  
Old September 10th 05, 06:30 PM
Tim
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Peter R. wrote:

Stan Gosnell wrote:


As others have said, the GPS will still work, you just won't be assured of
enough accuracy for the approach at MDA. You will still have plenty of
accuracy for holding at the MAP holding fix, though.



I think you mean only when there is a RAIM warning does the GPS still
provide course navigation. When I experienced a GPS error message with the
KLN-94, the GPS was completely useless and needed to be recycled before it
began working again, much like a computer hard-boot.

It is also worth noting that this particular error only happened this one
time with the KLN94. Having a few hundred hours now behind a GNS430, I
have never experienced any type of GPS system error or RAIM error with the
Garmin.

The new RNAV (RNP) criteria presume a complete loss of GPS for the
missed approach. If the airspace/obstacle environment will permit a
heading or track to a VOR missed approach in the event of loss of GPS,
then no backup is required. If the missed approach areas are too tight
then dual or triple IRUs are required.

With the present RNAV (GPS) approaches the presumption is that flying
headings will get you out of the woods until you can either get a vector
or receive a VOR. There is some risk with this presumption.
  #10  
Old September 10th 05, 07:40 PM
Ron Rosenfeld
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On Sat, 10 Sep 2005 17:30:27 GMT, Tim wrote:



The new RNAV (RNP) criteria presume a complete loss of GPS for the
missed approach. If the airspace/obstacle environment will permit a
heading or track to a VOR missed approach in the event of loss of GPS,
then no backup is required. If the missed approach areas are too tight
then dual or triple IRUs are required.


Where is that requirement spelled out for Part 91 operators using GPS
(single-sensor)? I don't see it in AC90-100, but that does not deal with
missed approaches.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)
 




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