I made it a habit for almost a year to read Dua el Ahd every morning. I will be traveling soon across the country with a completely different time zone and it will probably be a day and a half flights and transit to get there. How will I be able to read dua el ahd when I am on the plane? I mean which timezone do I abide by, my normal time zone, the current time on the plane, or the timezone of my destination place? Also my question is the same regarding prayer and which times/timezone do I abide by as I don't know how to find out the prayer times on a plane?

You go by the timing of your location. There are apps that help you with that. So determine your location and check the local timings for that location, and then pray based on that location’s timings and recite Dua Ahd in the morning of where you would be.