Apple is a forward looking company. They try to avoid supporting today's hardware standards 👿. They want to support only tomorrows standards 😀.
PCMCIA card adapters are certainly not on an ipad. ipads have never had usb ports. All input coming from outside the device is expected to come by wifi. [ You can connect the ipad to a computer for backup. There are some gps devices you can attach to the ipad. ]
You could try a pcmcia to usb adapter. You would then have to get the camera connection kit to attach to the ipad. You would then have to find some app to read the data on the pcmcia. You might be able to find some app in the app store that reads a flash drive. You would most likely be hijacking a proprietary app which would have not support and legal issues. All these adapters do not make for a reliable connection.
You could get a pcmcia card that included a wifi transmitter. There are some wifi storage devices that work with the ipad. Some of these wifi devices allow you to insert a usb flash drive. You could could look for a converter.
Perhaps you could look around for a pcmcia card that lets you fit in a camera card. You could then put the camera card into the camera connection kit. You would then have to look around for some app to read the data.
As the camera connection kit implies it is meant to read only files generated by cameras: pictures and videos. To read other file types you will need to buy or build an app.
I'd contact the aircraft manufacturer. Perhaps they are working on an adapter.
I think you are talking about some custom engineering job.
R