Air traffic control: the IBM 9020

Summary

Previously on Computers Are Bad, we discussed the early history of air traffic control in the United States. The technical demands of air traffic control are well known in computer history circles because of the prominence of SAGE, but what's less well known is that SAGE itself was not an air traffic control system at all. SAGE was an air defense system, designed for the military with a specific task of ground-controlled interception (GCI). There is natural overlap between air defense and air traffic control: for example, both applications require correlating aircraft identities with radar targets. This commonality lead the Federal Aviation Agency (precursor to today's FAA) to launch a joint project with the Air Force to adapt SAGE for civilian ATC. There are also significant differences. In general, SAGE did not provide any safety functions. It did not monitor altitude reservations for uniqueness, it did not detect loss of separation, and it did not integrate instrument procedure or terminal information. SAGE would need to gain these features to meet FAA requirements, particularly given the mid-century focus on mid-air collisions (a growing problem, with increasing air traffic, that SAGE did nothing to address). The result was a 1959 initiative called SATIN, for SAGE Air Traffic Integration. Around the same time, the Air Force had been working on a broader enhancement program for SAGE known as the Super Combat Center (SCC). The SCC program was several different ideas grouped together: a newer transistorized computer to host SAGE, improved communications capabilities, and the relocation of Air Defense Direction Centers from conspicuous and vulnerable "SAGE Blockhouses" to hardened underground command centers, specified as an impressive 200 PSI blast overpressure resistance (for comparison, the hardened telecommunication facilities of the Cold War were mostly specified for 6 or 10 PSI). At the program's apex, construction of the SCCs seemed so inevitable that the Air...