So again, what type of data (and data format) gets data onto a map? Is it a manual process, automated plotting process .... ? ... what "numbers" need rounding off? My feeling is there is some kind of automated plotter involved that makes a map, when and if someone desires or needs a map? Is the NWA search map Sluggo calls the FBI Map an instance of a computer plotted map which used McChord's radar data? What old computer language? SNOBOL? This is the same era we would have been using PL1 and other languages for computer plotted charts, (maps), etc... (The boxes of cards for a single run were prodigious!) I used PL1 and several other languages for data crunching here ... it was often so laborious it was almost defeating! MY guess is the military systems were more automated.
At the time, the country had an "air defense command" (at some point in time replaced by or absorbed into NORAD). Their job was to monitor the skies, especially around the periphery of the USA and Canada, for bombers from Russia or China, and to put fighters out to intercept bombers or anything that might be a bomber.
To do this, they could not just track enemy bombers. They had to track virtually
everything in the air and check off all those planes that were confirmed to be "friendlies." Whatever was left, then, were the suspected "bogies."
So they constantly tracked everything out toward the horizon, everything that had a transponder in operation, everything with a return signal strong enough to be more than a low altitude "general aviation" private plane.
everything They would have been tracking 305 to some degree even if 305 had not been hijacked.
To check off the "friendlies" the command's "direction centers" were in constant contact with FAA air traffic control centers. They constantly received flight plan data from the centers. They had hot lines so they could just pick up the phone and talk to flight controllers. They also had constant communication with direction centers (DCs) for adjacent regions so that known friendlies were passed from one region to another so that the second wouldn't have to go through the whole process of identifying the friendlies that came from the adjacent regions.
The command used "SAGE" to do this tracking. They got the
source data principally from cutting edge radar sites. The data was processed, then the resulting data was displayed, at the regional DC. For our flightpath plot, the radar site involved before the flight got down a ways into Oregon was the site at Mt. Hebo, OR. The DC was DC-12 at McChord. So I'll refer to them in the following explanation of how the system worked.
If I remember correctly, the radar antenna went around 6 times per minute. Each time it went around, a computery thing analyzed the video output from the radar set along with precise data (from the antenna sytem) on where the antenna was pointing. From this analysis the device produced very accurate digital information on the range from the antenna to the "target," the target's azimuth with respect to "true" north, and the precise time at which the range and azimuth were measured. The device was constantly doing this for practically everything in the sky.
The device would load this location/time info into a magnetic storage drum rotating in sync with the antenna. The device was constantly loading such info for all the things the radar saw in the sky. Each turn of the antenna the device also loaded the same kind of data for at least one fixed target at a precisely surveyed location.
When the device put the info on the drum, it sent a message over two parallel telephone lines to the DC at McChord. The essence of the message was, "Hebo has just made available for you position data for target "x" squawking "y."
Depending upon the speed of a target and what priority the DC placed upon tracking that target, the DC might not immediately respond "send it on over." In this case, the data stored on the drum for that target would be replaced the next time the antenna swept past the target. The data was updated in each rotation of the antenna.
Eventually the DC would request the data for our flight 305. The data would be sent, again, over two parallel telephone circuits. The part of the device that did this was the world's first modem.
The McChord DC had two digital computers doing exactly the same thing most of the time. One was "active" and the other "standby." They did this so that the center wouldn't go dead if a computer failed. The computers were the world's first operational digital computers.
The computers took the position/time data from Hebo and combined this with data the computer already had on the surveyed location of the Hebo antenna, the error in Hebo's alignment with true north, the known location(s) of the fixed calibration target(s), and the digital model of the earth to calculate location of the target with respect to earth coordinates.
When the coordinates were calculated, they were made available for viewing at the monitors of the various kinds of staff at the DC. On the monitors, the people would generally see a track of a few past positions and something like the current or latest position. They could call up the data for whichever target(s) they were interested in.
After calculating positions for a few times for a given target, they would have been able to project position forward in time. I haven't seen any indication that they actually did this. They would also have been able to smooth out "jitter" from errors in the data from Hebo. Again, I don't know if they did.
The calculated coordinates were not recorded. But the data coming in from Hebo was routinely recorded. They were also able to record such data for specific targets. They normally just recorded over the tapes. But, if someone said "reserve that tape" they would hold it for later analysis.
One important thing about the normal use of the tracking data is that the DC did not need to calculate target positions down to the yard. All they needed to do is know closely enough where a bogie was that they could get an intercepter fighter close enough that the fighter could see the bogie on its radar or by eyeball. Getting within half a nautical mile was close enough.
So they had a tape about 305. The people at the DC had no idea what to do to get 305 position history out of that tape. They were users of SAGE, not "techies."
Also at McChord was a detachment of techies. They routinely evaluated proposed changes to the programming. They routinely did QA checks of SAGE at McChord. They routinely did analyses related to "incidents." They were a detachment of the 84th Radar Evaluation Squadron ("RADES").
In much of the work they did, they would come into the McChord DC and take over the computer that was on standby. At times they'd run some evaluation version of the programming. They probably used the computer for running the analysis of the 305 data, because they were quite familiar with the computer. It is possible, however, that in 1971 they could have used a scientific calculator.
The analysis was calculation of 305 positions at exact minutes (no seconds). They certainly would have interpolated between positions at known times each side of the exact minutes. They calculated positions to a precision of 1 minute of latitude and longitude, probably because that's what the SAGE computer normally did because that's as close as the DC needed for its normal operation.
The coordinates were hand plotted on at least two paper charts. The red crosses do not have the uniformity that would come from a plotting machine.
