It's a piece of avionics http://www.avidyne.com/EX5000/default.shtm
that requires data uploads to keep its geographic and navigational databases current, and also dumps data from an engine monitoring application.
Both are done by plugging in the zip drive to the units front-panel usb port before powering up. It sees the drive and, if it has properly formated data on it, goes into its upload mode or, if it's blank, goes into its data dump mode. There is no way to access these routines otherwise. I've tried plugging in a flash drive instead, and the unit behaves as if nothing has been inserted.
Hm... What about those small usb drives that have micro hard drives in them? Those mount as hard drives and not as a "removable disk". Maybe that EX5000 just demands a physical disk and can't figure out flash media.
Just thought of something else too. The usb zip drive is powered externally so it doesn't require any power on the usb port. Are the usb ports on that devices powered (or under powered)?
That would definatly explain why a usb flash drive wouldn't work.
I am using a 1 GB Apacer flashdrive. It came with a utility by which I could make it appear as any kind of USB storage device, CD-Rom Zip Drive, HDD or what have you. Perhaps you should check out the web site of the manufacturer for similar compatible software.