[GreenKeys] FAA Teletypewriter Network 1959

[Jim Haynes]

I've posted about some of this before, so if it's repetitive please
skip it.

Service A is for surface weather observations.  Earlier these were made
by Weather Bureau people but mostly by CAA/FAA people at airports and
flight service stations.  Now I guess the observations are mostly
automated.  This has a long history.

At one time the observations were transmitted using Model 14 machines.
I know this only because Ray Morrison once showed me a bunch of the
machines he had I guess purchased from government surplus, and they
were all equipped with the weather symbol type and keyboard arrangement.

Later on transmission was from tape.  I don't know if the stations were
polled by machine or if the operators had to watch and transmit when their
turns came.  Later there was a box of relays called ASID for Automatic
Station Identification Device and it would transmit the station location
identifier - the 3-letter code such as is used for airports - and then
send the tape.  This involved a modified XD tape reader that could let
the distributor run without moving tape, so that it could generate the
code from the relays.  Then there was a system called SECO - Sequential
Control, which used SOTUS machines to recognize the station identification
letters during polling, and start the XD at the right time so the
operator didn't have to do anything to have the tape transmitted on time.
SOTUS is a Model 15 era machine that recognizes characters and sequences
of characters.

All this activity was done on several area circuits, with each airport
belonging to only one area circuit.  Then there was a system called
MEDIS for Message Diversion System that used FRXD machines to copy
certain weather from one area circuit to another, so that for example
Chicago and Los Angeles could have New York weather for what were then
long distance flights.

With the coming of jet air travel all this was much too slow and 
complicated.  FAA contracted with Teletype to make ADIS - Automatic Data 
Interchange System.  This involved changing all the area circuits to use 
Model 28 equipment, the stunt boxes taking the place of the SOTUSes.  The 
area circuits went from 60 to 100 wpm. A nationwide backbone circuit 
running at 1050 wpm linked through all the area circuits.  All weather 
data on the area circuits was copied to the backbone.  Switching centers 
copied selected out-of-area traffic off the backbone to the area circuits 
that needed it. All this copying and speed conversion was done with paper 
tape storage.

Service B was/is for flight plans and other messages directed to specific
stations rather than to all.  This used the selective calling feature of
Model 28 printers so that stations copied only the traffic intended for
them, while other traffic on the area circuits was ignored.  If you see
ex-FAA Model 28 printers most of them have a LOCAL/REMOTE toggle switch
on the base which operates a solenoid to override the selective calling
mechanism.  This allows printers to be swapped between Service A where
they copy everything and Service B where they copy only traffic addressed
to them.

Teletype developed a system for Service B and called it BDIS, a pun on
ADIS.  It used the same idea of a nationwide backbone and area circuits,
but different equipment for selecting which messages were copied from
the backbone to the area circuits.  This system used the DRPE high
speed punches.

Teletype was engaged to develop a system for Services C and O, naturally
called CODIS.  By this time the superiority of computer technology
switching systems was fully recognized and Teletype didn't get to build
CODIS.  I believe it used the Collins C-8400 computers.

 	---

 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man