Actually, YES, it's possible, with a few disclaimers. (1) You have to make sure that you set the Hero 4's "Auto-Off" option to NEVER. Then it'll stay on throughout the flight even though it's idle (as it must be without an SD card). (2) You must have iOS 11 or later installed on your iOS device. Follow the instructions for live screen capture on your device. (3) All you'll capture is the live video feed from the Hero 4, which is pretty low resolution. And you'll capture all the fits and hiccups that the live video feed is subject to. In other words, it'll look a LOT worse than what the Hero 4 would have been capturing on its SD card if you had one.