Re: It is getting easier

At 11:25 PM 11/14/96 -0800, Lucky Green wrote:
>If I remember correctly, some of the newer transponders used on 
>commercial aircraft actually transmit GPS data back to the controller in 
>real time. I wonder how long it will be before the FAA will include such 
>information in their database.

I don't think new transponders make much difference.  The old ones heighten
the radar image of the airplane which gives an accurate 2D position.  This
position is automatically entered into the FAA computer which maintains the
ATC controller's display.  In the old style, altitude is determined by an
altimeter on the airplane which encoded into the transponder signal.

If newer transponders are returning GPS signals, the position may be more
accurate (but probably not unless they can decode the selective
availability signal).  (OBCrypto for those who care.)


>"To obtain the position of any passenger flight in the US within 10 
>meters, click here."

In either case, the Passenger Name Records for the flight are in the
airlines databases (and have been there for many years), and the airplane's
physical position is in the FAA's computer (and has been for many years). 
The ability to find the current position of an airplane, or a passenger
remains dependent on the incentives and disincentives for database linking
and application development.  There are no insurmountable technical
problems.  The technical problems are those of getting old-technology
software to do something new.


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Bill Frantz       | The lottery is a tax on    | Periwinkle -- Consulting
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Bill Frantz sez:
> 
> At 11:25 PM 11/14/96 -0800, Lucky Green wrote:
> >If I remember correctly, some of the newer transponders used on 
> >commercial aircraft actually transmit GPS data back to the controller in 
> >real time. I wonder how long it will be before the FAA will include such 
> >information in their database.
> 
> I don't think new transponders make much difference.  The old ones heighten
> the radar image of the airplane which gives an accurate 2D position.  This

I missed how this got the 'Punk material, but a friend is running
parts of a test of this.

The en-route radar is roughly the same age as those IBM 360's in the
Centers that you keep hearing about. 

The current approach is radar, [?2 ghz] with interrogation of a
1 ghz transponder via the same array. The xponder has 4 octal digits
and {Mode C} the altitude from an accompanying encoding altimeter.

So the alternate approach is a GPS receiver with a transponder
replying to interrogations with position and altitude. For the most
part, in the "en-route" stage, the futzing by DOD is not a concern
-- all receivers in a given area are equally deceived. [Recall that
the goal is to avoid Delhi incidents.]

During departure and approach, the a/c will use 'differential GPS'
whereby a GPS RX at a known benchmark on the airport will broadcast
what error IT sees. [Errors are roughly linear within X mile zone.]
DGPS will be as good or better than many existing Instrument Landing
Systems, i.e. a few feet in all 3 dimensions...


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