Since scale is relative, world coordinates are usually expressed in units. Camera clipping is around 3,000 units by default so some FPS folks will equate meters with units.
If the fighter is a relatively unique item, you could add some exception coding. The better thing might be to add some ladder code and set a ladder next to the cockpit. [Jet jocks rarely use stairs or ramps. Also, some aircraft come with built-in ladders like the A-10.]
If you want the player to be able to walk on the jet model, things get a bit more complicated. You can either add code to detect both kinds objects or you can add a second matrix to represent the top of the aircraft. You can then use the current location/height of the character to determine which matrix to use as the ground height.
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TAZ
If you plan on using a second matrix for the figher, imagine a tarp thrown over the aircraft. That way a person could walk off the plane but not back on until they use the ladder again.