| s_anode@comcast.net 2006-09-30, 12:33 pm |
|
Mike wrote:
> Sam Wormley wrote: Since solar radio
>
> Won't RAIM address these issues for "life-critical" aviation systems?
>
> http://en.wikipedia.org/wiki/RAIM
Sam,
The extrapolation of a 3 to 6 dB C/No dip for a short period this past
solar peak to "all receivers on the sunny side of the earth will fail
for hours" is bad pseudo science at its worst. It would have been
more honest for them to have said that the 3 to 6 dB dip could happen
more often than once or twice every 11 years or that the dip could get
a couple dB deeper during the next cycle. But extrapolating predicted
(and somewhat speculative) estimates that say that the next solar peak
may be a little more active to there is going to be armageddon level
radio wave flares is bunk.
In addition, the statement about life-critical systems, implying a
direct hazard to life impact is not correct and demonstrates that the
authors are completely unaware of the hazard analyses associated with
aviation navigation. The critical safety aspect of WAAS is that the
system will not direct airplanes to fly into the ground. The hazard
that a WAAS approach becomes unavailable as it is being flown is a
"minor" hazard that would result in the execution of a missed approach
procedure if the weather is below the visual minimums. If weather is
below minimums and there isn't a non-GPS approach at that airport, the
pilot goes to his alternate airport. Not really any different than if
the weather falls below the precision approach minimums.
However, the author's point that GPS is vulnerable to interference and
solar storm effects does reinforce the recommendations that; a subset
of the existing ground based navigation aids need to be retained as a
backup, the transmit power on the GPS satellites should be increased,
and the number of satellites should be increased to provide a more
robust system.
Tom
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