There are two things here: the direction of the qiblah, and the prayer time.
About the first, you try your best to find the direction. These days it's relatively easy because most international flights (or flights longer than a few hours) have a navigation device in front of each seat which shows you which direction the plane is going. Try using that to find where the qiblah is. If you can do it, great, pray that way. If not, then do the best you can, and Allah SWT doesn't burden a soul more than it can bear. islamqa
Now about the prayer time, for three of the prayers (Fajr, Maghrib, and 'Isha) one can work out looking out the window whether the time for these has started or not. For the other prayers, estimate if you can, plan it out beforehand by looking up the prayer times at the place you will be above at that time, and if you can do neither, do the best you can again islamqa. And if you happen to learn later that you prayed before time, then offer it again.
And finally, Allah SWT has a concession for those who are travelling - you can combine Dhuhr and 'Asr, and you can surely tell looking out the window whether it's daytime or not.