Flieger Friday: MB&F HM9 Flow Air

MB&F HM9 Flow Air is by far the most expensive Flieger watch we have ever written about.  It is no surprise that it is a brainchild of genius Max Büsser, who stated in his previous interview to us that he is just living out his childhood fantasies of spaceships and mechanical toys.  His latest concept of Horological Machine No.9 (HM9), released in 2018, was brought to life with help of his professional friends, including design by talented industrial designer, Eric Giroud. The 2019 version is in 5N red gold with blackened movement and rhodium-plated balance wheels, limited to 18 pieces.

Max Busser MB&F

According to Max Büsser, HM9 Flow Air is inspired by the dynamic profile of mid-century aviation design.  The 1940s and 50s brought forth aircraft such as the sleek-bodied, snub-nosed De Havilland Venom that patrolled Swiss airspace for 30 years. Reminiscent of a jet engine, a highly complex case in alternating polished and satin finishes encloses a complex manual winding movement, developed fully in house. Independent twin balance wheels beat at a leisurely 2.5Hz (18,000bph) on each flank of HM9, visible under elongated domes of sapphire crystal. A third pane of sapphire crystal on the central body reveals the gearbox of the HM9 engine: a planetary differential that averages the output of both balance wheels to provide one stable reading of the time.


Sitting perpendicular to the rest of the HM9 engine is the dial indicating hours and minutes, driven by conical gears that ensure precise engagement even when motion is put through a 90-degree planar translation. The winding and setting crown is located on the rear of the central body, its deep fluting providing ergonomic grip as well as aesthetic coherence with the overall design. Two satin-finished air scoops are mounted alongside the pods containing the oscillating balance wheels, evoking the raised vents that allow continuous airflow to high-performance motor engines.

The case design of HM9 Flow had extreme curves and acute angles, which required new manufacturing techniques to obtain a complete milled and finished case. It consists of 49 components. When the MB&F team first brought the HM9 design to the manufacturing partners, the response was that these designs could not be manufactured. The case of HM6 Space Pirate was geometrically complex, but the maximum height differential (the vertical distance between contiguous points) remained within 5mm. With HM9, that differential doubled, creating radical curves that give the case its highly tactile presence.  It was also applicable to the mirror polishing and satin finishing, which required new tooling to reach the narrow crevices of the case.  A patent was filed for a three-dimensional gasket to ensure water resistance rating.


HM9 movement took three years of development and consists of 301 components.  It was created entirely in-house, with its double-balance with differential being like Legacy Machine No.2, even though they look nothing alike. The twin balance wheels of the movement feed two sets of chronometric data to a central differential for an averaged reading. The balances are made to impulse individually, and spatially separated to ensure that they beat at their own independent frequency of 2.5Hz (18,000bph) each. This is important to ensure a meaningful average, just as how a statistically robust mathematical average should be derived from discrete points of information. Another similarity with LM2 is the curved arms anchoring its balances.


This is by far an out-of-the-world flieger we have ever seen!  The dial is that of a traditional pilot watch with the proper aesthetics of a Type “A” flieger.  Yet, the dial is mounted vertically on this mechanical hull of a vintage airplane inspired case. The previous HM9 Flow was constructed in titanium case and limited 33 pieces. The latest 5N red gold is limited to 18 pieces with a price tag of $198,000 USD. One can only dream, or drool……

Learn More About MB&F HM9 Flow Air Here

Photo and Technical Details Credit: MB&F