Great Animation...
...but sadly I have to poke a few holes in this.
The script is a little robotic and a little bit cringeworthy. Although you spent a great deal of time with it I can't help but feel the drama in this piece is rushed.
It's good don't get me wrong - but I think the reason a few people have seen the drama as cheap is because it happens all too quickly - the viewer hasn't had enough time to connect with the characters to care when the drama and sadness starts to kick in.
I like the way you decided to keep the time and location a secret until the planes appear on the horizon - it's a very clever idea and one that would impact further if (like i mentioned before) you gave a little more time for the viewer to connect with the characters.
Fantastic choice in sound effects and music although it is a little choppy in places. Particularly when you change music tracks abruptly. Maybe look into fixing that?
The background art is beautiful. I love it. Simple yet stunning.