How Flying Works
How Planes Navigate With No Landmarks in Sight
On 23 July 1983, Air Canada Flight 143 — a Boeing 767, dubbed the “Gimli Glider” ever since — ran completely out of fuel at 41,000 feet over Canada, the result of a unit-conversion error during refueling (pounds calculated instead of kilograms). Both engines died. Most of the cockpit’s electronic displays went dark with them, leaving only basic stand-by instruments. Captain Robert Pearson, who happened to be an experienced glider pilot in his own time, worked out a glide profile using little more than judgment, airspeed and a known starting altitude, and brought the aircraft down 45 miles later on a disused air force runway at Gimli, Manitoba — no fatalities. It’s a dramatic illustration of a much less dramatic everyday fact: modern aircraft navigate constantly with no visible landmarks at all, over ocean, cloud and darkness, using systems built for exactly that problem.
Three real methods, three different eras
The oldest is dead reckoning — calculating position purely from known airspeed, heading, wind, and elapsed time since a known starting point, with zero external signal required. It's the method that got aviation through its earliest decades, and it's still taught today as a genuine backup skill, not a historical curiosity — exactly what Captain Pearson leaned on. Radio navigation followed: VOR (VHF Omnidirectional Range), rolled out widely from the 1950s, uses a network of ground beacons an aircraft measures its bearing from, which is precise but depends on being within range and line-of-sight of a transmitter — not much use hundreds of miles from land.
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The system that solved the ocean problem
The real breakthrough for long-haul, over-water flying was the inertial navigation system (INS), introduced to commercial aviation from the late 1960s onward. An INS is entirely self-contained — no radio beacon, no satellite, nothing external at all. Gyroscopes and accelerometers inside the unit continuously sense every acceleration and turn the aircraft makes, and from a precisely known starting position, the system integrates that motion data to keep calculating current position throughout the flight. It's the navigational equivalent of dead reckoning done automatically and continuously by machine rather than by hand, and it's exactly what let airliners fly confidently across oceans and polar routes with zero ground infrastructure beneath them for hours at a stretch.
Today, GPS has largely become the primary method for most navigation, offering precise position anywhere on Earth from satellite signals with no ground or self-contained system needed — but VOR and INS haven't disappeared. Both remain as deliberate, independent backups, because a system with no single point of failure is safer than relying on GPS alone, and because the aviation industry has learned, repeatedly, that redundancy in navigation is worth the cost of maintaining older technology that still works.
Sources & Further Reading
Common Questions
Frequently Asked Questions
Do pilots still use dead reckoning today?
Rarely as a primary method, but it's still taught and still genuinely useful as a backup — calculating position from known airspeed, heading, wind and elapsed time, with no external signal needed at all. The Gimli Glider crew leaned on exactly this kind of basic airmanship when their instruments went dark.
What's the actual difference between VOR, INS and GPS?
VOR is ground-based — a network of radio beacons an aircraft measures its bearing from, requiring line-of-sight to a transmitter. INS is entirely self-contained, using motion sensors to track position from a known starting point with no outside signal at all, which is why it kept working through the Cold War era over oceans with no ground beacons. GPS is satellite-based, offering precise position anywhere with no ground infrastructure needed, and has largely superseded the other two as the primary method, with VOR and INS retained as backups.
How did pilots cross oceans before GPS existed?
Mainly inertial navigation systems, introduced to commercial aviation from the late 1960s — self-contained units using gyroscopes and accelerometers to continuously calculate position from a known starting point, accurate enough for hours of ocean crossing with zero ground or satellite signal required.
Could the Gimli Glider crew see anything to navigate by?
Very little that mattered without power — most cockpit displays went dark when both engines failed, leaving only basic stand-by instruments. Captain Pearson, a qualified glider pilot in his personal time, used that background and simple dead-reckoning judgment, not any specialized navigation system, to work out the glide profile that got the aircraft to Gimli.