Vacuum fillers are known to tolerate flights well; that was part of their original sales proposition during the early jet era. Purportedly they can even write on an airplane, but I personally wouldn’t dare try.
The trick with flying with fountain pens is storage angle. The air pocket that remains in the pen is going to be at a much higher pressure than the air in the airplane, so it is going to expand. If the pen is stored nib up, that air pocket is close to the top, and can escape through the nib with minimal leakage. If the pen is stored nib down, the air pocket will expand and drive ink out of the nib.
The trick with flying with fountain pens is storage angle. The air pocket that remains in the pen is going to be at a much higher pressure than the air in the airplane, so it is going to expand. If the pen is stored nib up, that air pocket is close to the top, and can escape through the nib with minimal leakage. If the pen is stored nib down, the air pocket will expand and drive ink out of the nib.