Re: Faulty GPS data led to DART failure - article.

Hi Fafnir,

Thanks for that update. I thought that GPS was only certified for
"safety-of-life" critical operations when used with WASS which contains
extra integrity signals as in the quote below. Please correct me if I
am wrong.

http://gps.faa.gov/Library/waas-f-text.htm
"WAAS became operational for aviation safety-of-life use in the NAS on
July 10, 2003, providing en route navigation across the entire NAS and
vertical guidance performance (LPV) to most of the lower 48 states.
LPV performance enables pilots to descend with stabilized vertical
guidance to visibility minimums of ¾ mile and to altitudes as low as
250 feet above the runway."

But an in-orbit satellite is not in the NAS, and WASS corrections do
not apply.

http://gps.faa.gov/gpsbasics/GPSmodernization-text.htm
"A third civil signal, located at 1176.45 MHz (L5), will be provided
initially on GPS Block IIF satellites beginning in 2007, and continuing
with the Block III satellites scheduled for launch beginning in 2012.
This new L5 signal is protected worldwide for aeronautical
radionavigation use, and will support aviation safety-of-life
applications."

http://gps.faa.gov/gpsbasics/PresPolicy-text.htm
"... we have demonstrated the capability to selectively deny GPS
signals on a regional basis when our national security is threatened."

http://en.wikipedia.org/wiki/Galileo_positioning_system
"... The U.S. reserves the right to limit the signal strength or
accuracy of the GPS systems, or to shut down public GPS access
completely"
"... though GPS is now widely used worldwide for civilian applications,
it is a military system ... civil infrastructure, including aeroplane
navigation and landing, should not rely solely upon GPS."

http://www.caa.co.uk/docs/33/SRG_GAD_SSL25.PDF
"GPS must not be relied upon as a sole navigation reference in flight
critical applications."

In the original NS article the GPS data was used to overide the
inertial data thus making it the "sole navigation reference".

An interesting topic... Eddy [UK].

.

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