Longines Flyback Chronograph Turns 90: The Patent That Changed Aviation Timing

by Brent Robillard

Ubiquity breeds familiarity

The most successful watchmaking inventions often become so commonplace that we forget they were inventions at all. The rotating dive bezel. The GMT hand. The automatic winding rotor…

The flyback chronograph falls squarely into that category.

Today, if you spend enough time around pilot’s watches or military chronographs, you’ll eventually encounter the term. Most enthusiasts know what a flyback does. Fewer know who invented it. Fewer still know that ninety years ago today, on June 16, 1936, Longines secured patent protection for the mechanism that would become one of the most practical developments in chronograph history.

And that’s the sort of watch nerd fact that deserves a quick toast.

Longines flyback patent application from June 16, 1936

The purpose of the Flyback Chronograph movement

To appreciate the flyback, it helps to remember that aviation in the 1930s looked very different than it does today. Aircraft were travelling farther, navigation was becoming more sophisticated, and pilots increasingly relied on timing calculations throughout a flight. A chronograph wasn’t a luxury. It was a working instrument.

The problem was that a traditional chronograph could be cumbersome to use when timing successive intervals. To start a new timing sequence, the pilot had to stop the chronograph, reset it, and then start it again. Three separate actions. Three opportunities to make a mistake. Three moments where precious seconds disappeared.

The flyback solved that problem elegantly. With a single press of a pusher, the chronograph hand would instantly return to zero and begin timing again without stopping the movement. What sounds like a small mechanical trick was actually a significant improvement in usability. When you’re flying an aircraft and trying to maintain a course using dead reckoning, simplicity is key. And Longines understood that.

A document that would change aviation timing

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The Patent That Started It All

While production examples had already begun leaving Saint-Imier in 1934, Longines filed its patent application for the flyback chronograph on June 12, 1935. The patent was granted the following year and officially published on June 16, 1936.

That date here is important because it effectively secured Longines’ place in chronograph history. The patent protected the company’s invention for fifteen years and gave the brand a considerable advantage at a time when aviation technology was advancing rapidly.

Looking back today, it’s easy to view the flyback as an inevitable development. At the time, however, it represented a genuinely useful solution to a very real problem. And, well… the best watchmaking innovations usually do.

Enter the 13ZN

If the patent established the concept, the 13ZN made it legendary. Among vintage chronograph enthusiasts, the Longines 13ZN occupies almost mythical territory. Introduced in 1936, it brought the flyback function into serial production and quickly established itself as one of the finest chronograph movements of its era.

Collectors have spent decades praising the 13ZN for its architecture, reliability, proportions, and finishing. Even today, it remains one of the most sought-after vintage chronograph calibres on the market.

Part of its appeal comes from the fact that it wasn’t produced for very long. Part comes from its historical importance. And part comes from the simple reality that it is just an exceptionally good movement.

Many examples found their way to Italy and the United States during the interwar period, where aviation was developing at breakneck speed. Among the notable users was famed American aviator and Antarctic explorer Richard Byrd, who relied on a Longines flyback chronograph during his Antarctic expedition of 1939-40.

That’s the sort of provenance collectors dream about.

Longines Flyback Chronograph “Tre Tacche” (1942, ref. 4974)*: 37.5 mm stainless-steel case with screw-down back, powered by the 13ZN Flyback chronograph calibre and a black radium dial.*

The Flyback Lives On

What I find interesting is that the flyback never became a historical curiosity. Some watchmaking inventions are fascinating, but ultimately obsolete. The flyback isn’t one of them. Not really.

In fact, Longines has arguably done more than most major brands to keep the complication relevant in modern watches.

Over the past few years, we’ve had the opportunity to spend time with several models from the Spirit collection, including a number of flyback-equipped chronographs. The Spirit line has consistently impressed me because it manages to draw from the brand’s aviation history without feeling trapped by it.

Check out these contemporary flyback chronos from Longines:

Longines Spirit Flyback in 18K Gold

Longines Spirit Flyback Titanium

Longines Spirit Flyback

One of my personal favourites from 2025 was the Spirit Pilot Flyback. The compact case, hand-wound movement, and straightforward execution made it one of those watches that tapped into brand history without being trapped by it. It also earned a spot on my Best Watches Under $10K list for 2025.

The current Spirit Flyback models use modern column-wheel chronograph movements with silicon balance springs, COSC certification, and lengthy power reserves. They are contemporary watches by every measure, but the core idea remains unchanged from the one Longines patented ninety years ago.

Push the button.

Reset.

Restart.

Keep moving.

Longines Spirit Pilot Flyback @calibre321

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A modern incarnation of the flyback movement @calibre321

A Small Piece of Watch History Worth Remembering

Most anniversaries in watchmaking involve a new limited edition or a commemorative dial colour. This one is a little different.

Ninety years ago today, Longines secured protection for a mechanism that would go on to influence generations of pilot’s watches and chronographs. The flyback wasn’t designed to be complicated. It was designed to make a pilot’s job easier.

That’s probably why it has survived. Good ideas tend to do that.

And while most people outside our little corner of the hobby probably won’t care that today marks the ninetieth anniversary of the flyback patent, watch enthusiasts have always been drawn to these stories. Because sometimes the most interesting part of a watch isn’t what’s on the dial. It’s the idea hidden underneath it.