I saw your case and I found 2 differences than the tutotial:
For Wall boundary condition of Aircraft, you need to use No-Slip condition for velocity and not “Zero Gradient”. While Zero Gradient condition is to be used with Temperature and not “a fixed value”. This is most likely cause of failure of your simulation as you are trying to simulate the aircraft with Neumann BCs.
Either in Bottom wall or Top wall, I guess you have used T= 293K. I am not sure. But anyways it just for your correction. I do not think it will pose any error though.
I have tried your simulation and they are running good now. THe link to the project is:
I hope this helps. All the very best.