How Flying Works
How Planes Navigate With No Landmarks in Sight
On 23 July 1983, Air Canada Flight 143, a Boeing 767 known ever since as the “Gimli Glider”, ran out of fuel at 41,000 feet over Canada. The cause was a unit mistake during refuelling: pounds were calculated instead of kilograms. Both engines stopped, and most of the cockpit’s electronic displays went dark with them, leaving only basic standby instruments. Captain Robert Pearson was an experienced glider pilot in his spare time. Using little more than judgment, airspeed and his known starting altitude, he planned a glide and landed about 17 minutes later on a former air force runway at Gimli, Manitoba. Nobody died. It’s a dramatic example of a quite ordinary fact: modern aircraft navigate all the time with no visible landmarks, over ocean, cloud and darkness, using systems built for exactly that.
Three real methods, three different eras
The oldest method is dead reckoning. You work out your position from known airspeed, heading, wind and the time since a known starting point, with no outside signal at all. It carried aviation through its early decades, and it’s still taught as a real backup skill, not a historical curiosity. It’s exactly what Captain Pearson relied on. Radio navigation came next. VOR (VHF Omnidirectional Range), rolled out widely from the 1950s, uses a network of ground beacons that an aircraft measures its direction from. It’s precise, but only within range and line of sight of a transmitter, so it’s little use hundreds of miles from land.
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The system that solved the ocean problem
The real breakthrough for long flights over water was the inertial navigation system (INS), which reached commercial aviation from the late 1960s. An INS is completely self-contained: no radio beacon, no satellite, nothing outside the aircraft. Gyroscopes and accelerometers inside the unit sense every acceleration and turn the aircraft makes. Starting from a precisely known position, the system adds up all that movement to keep calculating where the aircraft is. It’s dead reckoning done automatically and continuously by a machine. That’s what let airliners cross oceans and polar routes confidently for hours with no ground equipment beneath them.
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Why flight paths curve on a flat map
The Earth is a ball, so the shortest path between two cities, the great circle (blue), looks curved when the globe is flattened into a map. The line that looks straight on the map (dashed) is actually longer: for JFK–HKG it’s 16,399 km against 12,970 km, 3,428 km of extra flying. That’s why flights from New York to Asia head north over the Arctic. Real routes also bend for winds and airspace. Distances calculated from airport coordinates.
Today GPS is the main method for most navigation. It gives a precise position anywhere on Earth from satellite signals alone. VOR and INS haven’t disappeared, though. Both stay on as independent backups, because a system with no single point of failure is safer than relying on GPS alone. Aviation has learned many times over that backup navigation is worth the cost of keeping older technology that still works.
Satellite approaches through the mountains: Queenstown
Satellite navigation did more than replace ground beacons. It let aircraft fly curved, precise paths that older systems could never draw.
The standard for this is called RNP, required navigation performance. It means the aircraft must prove it is staying within a set distance of its planned path, for example 0.3 nautical miles, and alert the crew if it can’t. Combine GPS, inertial navigation and that self-monitoring and a jet can follow a narrow corridor along a valley.
Queenstown in New Zealand became the showcase. The airport sits among steep mountains, and low cloud often forced flights to divert. Qantas began RNP approaches and departures there with Boeing 737-800s in September 2004.
The aircraft follow a curving path between the mountains, set in the flight computer, instead of needing a long, straight line to a ground beacon. The result was lower minimums, meaning flights can land in worse weather, and fewer diversions.
Sources & Further Reading
Common Questions
Frequently Asked Questions
Do pilots still use dead reckoning today?
Rarely as the main method, but it’s still taught and still useful as a backup. You work out your position from known airspeed, heading, wind and time elapsed, with no outside signal at all. The Gimli Glider crew relied on 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 that an aircraft measures its direction from. It needs line of sight to a transmitter. INS is completely self-contained. It uses motion sensors to track position from a known starting point, with no outside signal, which is why it worked over oceans with no ground beacons. GPS is satellite-based and gives a precise position anywhere, with no ground equipment needed. It has largely replaced the other two as the main method, and VOR and INS are kept as backups.
How did pilots cross oceans before GPS existed?
Mainly inertial navigation systems, which reached commercial aviation from the late 1960s. These self-contained units use gyroscopes and accelerometers to keep calculating position from a known starting point. They’re accurate enough for hours over an ocean with no ground or satellite signal at all.
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 standby instruments. Captain Pearson flew gliders in his spare time. He used that experience and plain flying judgment, not a special navigation system, to plan the glide that got the aircraft to Gimli.
Last reviewed: October 2026. Facts that change, such as fleets, airspace and airline ownership, are re-checked on a schedule. Spotted an error? Email contact@skyplus.news and we’ll fix it. See how we check facts.