Clarification about the term "GPS Shutdown"

[Juergen Nieveler]

In free countries with elected governments, the elected officials are in
fact very concerned with complaints they receive from the electorate.

In my experience, the only thing elected officials REALLY are concerned
about is not getting caught.


Juergen Nieveler

 

[Alan Browne]

Long term outage affecting those in flight? hmmmm....

"attention paasengers, you may notice a large plane nearby. no, it's
not an escort. please remain calm, we're gonna stick it out for another

TCAS alerts will keep the a/c well seperated in any case (in the context of the
fantasy under discussion).

 

[Alan Browne]

Presumably they'll switch off the transmitter for the civilan
frequency while leaving the military one on?

The fly in that soup is that a P/Y code receiver when turned on needs get the
Handover Word (HOW) from the C/A code in order to set the correlator for P/Y
code. (C/A means "Coarse/Acquisition") That's a 7 day long code... without the
HOW, hard to jump in. I suppose if the time is known accurately that the HOW
can be seperately estimated and correlation might occur.

 

[Mxsmanic]

This is one of those cases where experimentation isn't needed. Perhaps you
need a brain?

Sometimes experience is the best teacher. Try it and see. Send your
200 balls down the bowling alley and see if they touch each other.

 

[Mxsmanic]

TCAS alerts will keep the a/c well seperated in any case (in the context of the
fantasy under discussion).

Rather like bumper-car navigation.

 

[Alan Browne]

Mark McIntyre writes:




Sometimes experience is the best teacher. Try it and see. Send your
200 balls down the bowling alley and see if they touch each other.

You don't have a very good sense of scale.

A 747 measures some 230 feet in length.
10 minute separation at 500 knots = 83.3 NM = 506343 feet apart.
Or about 2201:1

Laterally, 60 NM separation = 364567 feet apart. (1585:1)

Google informs us that a bowling lane is 63 feet long, and that a bowling ball
is 27 in. (circ) which is about 9 inches (0.75 feet). 84:1.

So, for your analogy to work, the bowling ball lanes would have to about 1650
feet long, and 1189 feet wide. This would accomodate one bowling balling ball
in one lane and another in another lane laterally and/or a bowling ball at the
begining of a lane just as another reaches the end and they're both traveling at
the same speed.

 

[Alan Browne]

Alan Browne writes:




Rather like bumper-car navigation.

TCAS is a warning system, not a navigation system. Remember, this is a 'fantasy
situation' where not only has something unlikley occured, but two aircraft have
to drift laterally and exactly towards each other for many hours at the worst
possible drift rate.

The display will show aircraft that are 30 NM and more away. So, if two
aircraft are drifting towards each other at 2 NM/hr, both aircrews will have 7.5
hours to ponder the situation.

(Min. surv. requirement is 14 NM, so 3.5 hours to ponder the situation.)

 

[Juergen Nieveler]

TCAS alerts will keep the a/c well seperated in any case (in the
context of the fantasy under discussion).

Unless the ATC interferes, of course - like over Lake Constance a few
years ago.


Juergen Nieveler

 

[Mxsmanic]

The display will show aircraft that are 30 NM and more away. So, if two
aircraft are drifting towards each other at 2 NM/hr, both aircrews will have 7.5
hours to ponder the situation.

And if they are facing each other, they'll have 90 seconds.

 

[Alan Browne]

Unless the ATC interferes, of course - like over Lake Constance a few
years ago.

The outcome of that investigation is that the controller gave an instruction
that was to be the cause of the collision. Had the Russan crew and the DHL crew
both obeyed their TCAS and ignored the controller, the collision simply would
not have occured. This was the first 'accident' involving TCAS... because it
was ignored, not obeyed, by the Russian crew. I won't state that Russian pilots
are perhaps more prone than western pilots to obey controllers, but the thought
does cross my mind.

"TCAS Worked as Advertised
German investigators have released some details of the cockpit voice recorder
(CVR) tape that revealed both aircraft TCAS systems were issuing traffic
warnings with the Tupolev crew hearing “Climb, climb...” simultaneous to the 757
crew hearing, “Descend... descend...” According to the CVR, the crew of the
Tu-154 received conflicting instructions almost simultaneously. Within seconds
of getting their initial TCAS resolution advisory (RA) to climb, the Swiss
Skyguide controller instructed them to “descend Flight Level 350, expedite, I
have crossing traffic.""
http://www.ainonline.com/issues/08_02/08_02_germancollpg16.html

"Some 45 seconds prior to the collision pilots of the Boeing and Tupolev, still
almost 11 km apart, both received commands from their collision avoidance
systems to change their altitude: Boeing was to descent and the Tupolev was to
gain altitude. However, at the same instant the pilot of the Tupolev received a
contradictory order from the air traffic controller (ATC) to descent.

After a few seconds of executing the ascent maneuver, as ordered by the TCAS II,
and the second order from the ATC to descent Tu-154M crew decided to follow the
ATC instructions instead and begun dropping altitude. At the time of the
collision both aircraft were in descent: the Boeing was following TCAS II
commands and the Tupolev was following ATC orders."
http://www.aeronautics.ru/news/news002/news053.htm

Further, the Swiss control center was undermanned at the time for the workload
and their own collision avoidance computer was down. "The second controller
assigned to assist the controller in charge was on break." -1st link above

It gets better: a German controller could see it coming... " At the same time, a
controller for Germany’s Deutsche Flugsicherung (DFS), who was on duty in the
Karlsruhe ATC center, observed the conflict. The DFS controller repeatedly tried
to call Skyguide, but the telephone was initially busy and then went unanswered.
It was learned that Skyguide’s primary telephone line was out of order and the
Skyguide controller was using the reserve phone line up to two minutes prior to
the accident, attempting to call the tower at Friedrichshafen."

In an aviation accident there is rarely a single cause of an accident. It is
almost always a chain of little errors and discrepencies that lead to the
disastrous conclusion.

 

[Alan Browne]

if you read for comprehension, you'd have realised Alan's remark was
addressing your statement.

Mx' replies are calculated misdirections, ducks, misquotations, selective
snipping and out of context parries. I've known him in the usenet universe for
a few years (photo stuff). His usenetiquette there is of the same style.

 

[Alan Browne]

Alan Browne writes:




And if they are facing each other, they'll have 90 seconds.

//sigh// Many posts ago, it was explained to you that aircraft at given flight
level are all flying in the same direction in oceanic space. This altitude is
measured by barometric altimeters, all calibrated every 6 months and all set to
the same reference pressure (QNE / 1013.3 mb / 29.92" Hg.). Aircraft travelling
in the opposite direction are 2000' above and 2000' below (above FL 290). Below
FL290, the separation is 1000'.

When RVSM qualified altimeters become standard equipment on all aircraft, then
above FL290, the vertical separation minimum will be reduced to 1000' allowing
more aircraft into the system. This is GPS independant, of course.

Hence, the collision of aircraft fore and aft is all but impossible, the
collision of aircraft drifting laterally into each other extremely unlikely for
the reasons stated. And in which case, TCAS will be there to alert both crews
with more than amply time to act.

 

[Dave Baker]

You're too polarized in your thinking and you haven't named a single thing that
is so GPS dependant that it will fail totally.

Ok, how about my entire business - long range tracking of ships at sea using
GPS for positioning & Inmarsat D+ for data link.

One day the manufacturers of this equipment will hopefully have a version of
the transponder that runs on Galileo as well as GPS, but not at the moment.

There is no other system that gives us the accuracy we need over the coverage
region that we need for the price we need.

Dave

The email address used for sending these postings is not valid.
All replies to the group please.

 

[Alan Browne]

Secondly, the INS does automatically accept large changes in position,
velocity or fot that matter Range/Range-rate data from the GPS.

ooops/// that's "does not automatically accept"

 

[gomez]

Ok, how about my entire business - long range tracking of ships at sea using
GPS for positioning & Inmarsat D+ for data link.

Er , *why* do you do long range tracking of ships at sea? Its not a
business model in itself.

 

[tallen]

It an IMO requirement and after 31 Dec 04 all vessels over 300
tons....many convoluted exceptions re: freight, flag, country of origin,
ports visited etc. etc. the USCG will require AIS on just about all
commercial vessels over 65 feet, ships registered for over 150
passengers, and tow vessels over 26 feet and 600 hp used domestically
and entering from foreign waters.

And whoever said the US Government used business models?

T

 

[Alan Browne]

It an IMO requirement and after 31 Dec 04 all vessels over 300
tons....many convoluted exceptions re: freight, flag, country of origin,
ports visited etc. etc. the USCG will require AIS on just about all
commercial vessels over 65 feet, ships registered for over 150
passengers, and tow vessels over 26 feet and 600 hp used domestically
and entering from foreign waters.
And whoever said the US Government used business models?

That has nothing to do with what would happen in the unlikely event that GPS
gets shutdown. You will continue to receive position reports (less often, less
accurate) but it won't prevent operations, but may slow them down. IOW, in the
'emergency' of no GPS signal, other activities will adapt to the emergency ...
the world will not end.

Cheers,
Alan

 

[Dave Baker]

Er , *why* do you do long range tracking of ships at sea?

Because ship owners like to know where their assets are.

Especially when they are not where they are supposed to be.

Dave

The email address used for sending these postings is not valid.
All replies to the group please.

 

[Dave Baker]

the world will not end.

Well, I don't think anyone suggested it will. However, if you think a lot of
money won't be lost, then you are incorrect.

Dave

The email address used for sending these postings is not valid.
All replies to the group please.

 

[tallen]

Alan,
You are correct regarding a GPS shutdown. The AIS system integrates GPS
along with radar and electronic compass outputs and other required
vessel specific information such as contents, crew nationality, port of
last call, to improve tracking capabilities and ship to ship near
proximity safety information.

Aside the negative effect on bridge operations, I suspect that given the
current state of affairs...(called "homeland security"), the loss of
real time locational data would cause our marine security agencies to
implement heightened measures regarding VTS and other inbound controls
that would cause a slow down vessel movement, inspections, and port
operations.

In my previous e-mail, I was commenting somewhat tongue in cheek
regarding gomez's question with respect to the US Government....

"Er , *why* do you do long range tracking of ships at sea? Its not a
business model in itself."

A little holiday levity on my part. I did not comment on GPS utilization
or lack thereof. Others have commented on the positive attributes of
the commercial/private business model.

T