Is the headset adapter compatible with the GoPro case or does the case need to be modified to allow the cable to connect?
It is not compatible with the waterproof case as it is completely sealed but will work with the GoPro Frame (11-11396).
Will this Pilot USA Hero 3 adapter also record ATC communications?
Yes, this will record both intercom and ATC communications.
Must this adapter be used in conjunction with a headset or will it still collect all ATC and intercom audio if plugged in to an unused intercom jack?
This adapter is to be used inline with your headset to record.
Is the jack on this Pilot USA GoPro Hero 3 to Dual GA Headset adapter a 6.3 or a 3.5mm?
This adapter is neither 6.5 nor 3.5mm. The end that goes into the GoPro camera is Mini USB and the other end is the standard GA headset jack connection.
Is this Pilot USA GoPro Hero 3 to Dual GA Headset Recording Apapter a coiled cable or a normal straight cable?
Some portions of this cable are coiled and some are straight. If you click on the photo on this page you can see a zoomed in view of the product which shows this.
Is this compatible with GoPro Hero 4 cameras? Also, will I need any other accessories to record Radio/ATC?
Yes, this adapter is compatible with the GoPro Hero 3, 3+, and 4 cameras. No, you simply plug this adapter into the camera and the other end inline with your headset and it will record communications.
How long is this Pilot USA GoPro Hero to Dual GA recording cable?
This cable is approximately 45" long. One of the sections is coiled it so it can be extended further when needed.