When approaching runway 23 via golf taxiway for departure in the skyhawk just as you turn left onto the runway the aircraft falls through the earth. It will tumble and over speed warnings commence.
Clear scenery catch in settings and restart device :)
It happened to me once and I did what @Joeoreilly77 said.
You might just wanna go to bed about it :)
Try the above, you can try restarting the app, and in the worst case scenario delete and re install infinite flight.
Falling through the earth is a known issue which can be easily fixed by doing what @Joeoreilly77 said.
Look at the support FAQ, they addressed your concern.
Remember, you should always look at the support FAQ before posting in support.
Anyways clearing the scenery cache should solve the problem.