I’m really intrigued by this. The idea of a large creature in the desert with blue eyes appeals to me in a “I’m tired of all the monsters having red eyes” kind of way. I’m left wondering if the creature is of supernatural origin or if its a mutated strain of something, possibly from a nearby test site.
Anyway, since this is meant as a prologue, what if you told it from the airman’s point of view instead of your narrrator? Then you could have more freedom setting the scene, building suspense, etc. You could create all sorts of tension while he is trying to determine what he is looking at. Somehow the fact that he can see it out there for a while before it even notices him adds to the scare/suspense and should be played up. I say this because the formula is usually the creature stalks the person long before the person knows it’s there. The fact that he sees it, but can’t make it out is good. Then when it finally notices him, turns toward him, and charges could be a big moment. Even if the rest of your book is from the 1st person POV of your narrator, I think you could tell this story third person POV from the airman since it’s a prologue. Then in chapter 1, switching to your narrator, you could still mention the “tale” of the airman in the desert to let your reader know the narrator is familiar with the story.
I would like to see more of this.