What does the "7th arc" mean in Australian English?

[Liam O'Connor]

I'm trying to figure out what the term, 7th arc, means
in Australian English.

I find many references to it in this detailed document:
http://www.atsb.gov.au/media/5243942/AE-2014-054_MH370_SearchAreasReport.pdf

But, the details obscure the meaning to me.

Do you have a simple summary of what the Australians
mean when they speak about a "7th arc"?

[Peter T. Daniels]

On Monday, June 30, 2014 9:48:47 PM UTC-4, Liam O'Connor wrote:

> Do you have a simple summary of what the Australians
> mean when they speak about a "7th arc"?

It hasn't changed since the thread started by someone calling himself
"Daniel Webster" was last added to about 18 hours ago.

[Steve Hayes]

On Mon, 30 Jun 2014 18:48:47 -0700, Liam O'Connor <liamo...@example.com>
wrote:

>I'm trying to figure out what the term, 7th arc, means
>in Australian English.

Haven't we already discussed this in another thread?



--
Steve Hayes from Tshwane, South Africa
Web: http://www.khanya.org.za/stevesig.htm
Blog: http://khanya.wordpress.com
E-mail - see web page, or parse: shayes at dunelm full stop org full stop uk

[Snidely]

Steve Hayes presented the following exclamation:

> On Mon, 30 Jun 2014 18:48:47 -0700, Liam O'Connor <liamo...@example.com>
> wrote:

>> I'm trying to figure out what the term, 7th arc, means
>> in Australian English.
>
> Haven't we already discussed this in another thread?

While Liam has posted here before, maybe he's not a regular reader, and
the other thread may be out of sight ... he doesn't seem to be using
GG, so he might not be seeing threads ordered by mostly recently
added-to, but merely most recent started.

/dps

--
Maybe C282Y is simply one of the hangers-on, a groupie following a
future guitar god of the human genome: an allele with undiscovered
virtuosity, currently soloing in obscurity in Mom's garage.
Bradley Wertheim, theAtlantic.com, Jan 10 2013

[Ross]

It doesn't mean anything special in Australian English. "Seventh" and "arc"
mean the same thing as in any variety of English. In order to understand
what the "7th arc" is, you have to read some of the history of the search
for the Malaysian plane. As briefly as possible, the "arc" is a line on
the map showing possible locations of the plane as determined by a signal
received at a particular time by a satellite.

[Peter Duncanson [BrE]]

On Tue, 1 Jul 2014 02:52:02 -0700 (PDT), Ross <benl...@ihug.co.nz>
wrote:

Yes.

There were 7 "handshakes" between the plane's staellite communication
unit and the INMARSAT ground station via the satellite. Using
information about the radio signals for each handshake it was possible
to calculate the distance between the plane and the satellite and
thereby to draw a circle on the Earth's surface (with the satellite's
ground zero in the centre). So they were 7 circles. Most parts of each
circle were impossible as locations for the plane (too far away). That
left an arc of each circle as feasible locations. Hence 1st, 2nd, ...
7th arc.

The 1st handshake was initiated by the aircraft. It was a log-on to the
satellite communications system. The next 5 handshakes were "log-on
confirmations" initiated by the ground station. The 7th was a new log-on
request initiated by the aircraft (currently presumed to have resulted
from interruptions to the electricity supply caused by fuel exhaustion
and then the last-resort generator being automatically deployed).


--
Peter Duncanson, UK
(in alt.usage.english)

[Liam O'Connor]

On Tue, 01 Jul 2014 02:13:06 -0700, Snidely wrote:

> While Liam has posted here before, maybe he's not a regular reader, and
> the other thread may be out of sight ... he doesn't seem to be using
> GG, so he might not be seeing threads ordered by mostly recently
> added-to, but merely most recent started.

I apologize. I had not known about the other thread.
I'm using a LIFO sort on my newsreader.
Please ignore this thread.

[Mill Jones]

On Tue, 01 Jul 2014 12:44:01 +0100, Peter Duncanson [BrE] wrote:

> So they were 7 circles. Most parts of each
> circle were impossible as locations for the plane (too far away). That
> left an arc of each circle as feasible locations. Hence 1st, 2nd, ...
> 7th arc.

The whole point of the 7th arc is that the search is /perpendicular/
to the circle!

Hence, the farthest northern perpendicularity segments the arc, while
the farthest southern perpendicularity delimits that perpendicular segment.

There is no need to search further along the line of search, so the
circle, becomes a delimited arc.

The important factor is that the 'term' 7th arc, indicates a search where
the direction of travel of the object being searched for is explicitly
perpendicular (or at least *different*) than the inherent line of search.


--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---

[John Varela]

On Tue, 1 Jul 2014 16:19:43 UTC, Mill Jones <mill...@comcast.net>
wrote:

> On Tue, 01 Jul 2014 12:44:01 +0100, Peter Duncanson [BrE] wrote:
>
> > So they were 7 circles. Most parts of each
> > circle were impossible as locations for the plane (too far away). That
> > left an arc of each circle as feasible locations. Hence 1st, 2nd, ...
> > 7th arc.
>
> The whole point of the 7th arc is that the search is /perpendicular/
> to the circle!

What makes you think that? The airplane's track could have been
tangent to the circle or anything in between that and radial.

--
John Varela

[Peter Duncanson [BrE]]

On Tue, 1 Jul 2014 16:19:43 +0000 (UTC), Mill Jones
<mill...@comcast.net> wrote:

>On Tue, 01 Jul 2014 12:44:01 +0100, Peter Duncanson [BrE] wrote:
>
>> So they were 7 circles. Most parts of each
>> circle were impossible as locations for the plane (too far away). That
>> left an arc of each circle as feasible locations. Hence 1st, 2nd, ...
>> 7th arc.
>
>The whole point of the 7th arc is that the search is /perpendicular/
>to the circle!
>

The search is along the arc of the circle. When searching for possible
wreckage on the suface they make an allowance for "drift" caused by
ocean currents and wind.

>Hence, the farthest northern perpendicularity segments the arc, while
>the farthest southern perpendicularity delimits that perpendicular segment.
>
>There is no need to search further along the line of search, so the
>circle, becomes a delimited arc.
>
>The important factor is that the 'term' 7th arc, indicates a search where
>the direction of travel of the object being searched for is explicitly
>perpendicular (or at least *different*) than the inherent line of search.
>
>
>--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---

--
Peter Duncanson, UK
(in alt.english.usage)