Great circle navigation represents one of the enduring technical fundamentals of long-range flight planning, and the question of how pilots historically plotted and flew these routes before satellite navigation and flight management systems touches on a discipline that shaped an entire generation of professional aviators. A great circle is the shortest path between two points on a sphere, and because the Earth is a sphere (or more precisely, an oblate spheroid), the shortest route between two distant points—say New York and Tokyo—does not follow a constant compass heading. Instead, it curves relative to the meridians, meaning the aircraft's true heading changes continuously throughout the flight, even though the airplane is flying the most direct possible path. This is why polar routes look so dramatically curved on flat Mercator projection maps despite being the shortest distance between two points.
Before the FMS/GPS era, navigators solved this problem using exactly the faceted-arc approach the original poster intuited. Great circle routes were broken down into a series of rhumb line segments—legs of constant magnetic or true heading—typically plotted at intervals of 5 to 10 degrees of longitude or at regular time/distance intervals. Navigators used pre-computed great circle charts, gnomonic projection charts (on which great circles appear as straight lines, making initial plotting far easier), or great circle sailing tables and slide-rule-style computers to calculate the coordinates and initial heading for each waypoint along the route. The E6B flight computer, celestial navigation fixes, and later inertial navigation systems (INS) were the tools of the trade for oceanic and polar crossings from the 1950s through the 1990s. A navigator, or in later years the pilot using an INS/IRS unit, would input a string of waypoints—lat/long coordinates—and the system would command incremental heading changes between each segment, effectively "flying the arc" as a series of straight-line chords approximating the true curve. The more waypoints used, the closer the flown path hugged the actual great circle.
This matters to today's professional pilots because the underlying physics and math haven't changed—only the automation has. Modern FMS units perform this same great-circle segmentation instantaneously, computing continuously updated heading and track guidance between waypoints defined by RNAV/RNP procedures, oceanic tracks, or NAT/PACOTS structures. Pilots flying long-haul international routes still benefit from understanding why their track appears curved on a map display while the aircraft is flying the shortest distance, and why oceanic clearances specify a string of lat/long coordinates rather than a single heading. This knowledge is directly relevant to understanding CPDLC oceanic clearances, contingency procedures, and how the aircraft's lateral navigation mode sequences between waypoints, including how wind correction angles are applied dynamically along a curving track.
More broadly, this topic reflects the larger arc of navigation technology in aviation—from celestial fixes and dead reckoning, to INS and Doppler radar, to GPS and satellite-based augmentation, to today's RNP-AR approaches with curved paths flown to tight containment. Understanding the manual, mathematical origins of great circle navigation gives working pilots a deeper appreciation for why automation behaves the way it does, and reinforces the airmanship principle that automation should be understood, not just trusted. This kind of foundational knowledge remains a staple of ATP written exams and transport-category type ratings precisely because failures of GPS, FMS, or INS equipment still occasionally require pilots to fall back on manual plotting techniques, particularly on long oceanic or polar segments where backup navigation procedures remain part of operational contingency planning.