Frederick Libby, like many other airmen, got into aviation because it sounded better than the infantry. In Libby’s case, it was the rain that got to him; he felt sorry for the men entrenched in what had been a swampland, since the Germans across from them had seized the ridge. Whatever else he knew, he knew airplanes didn’t fly in the rain.
Except that sometimes they did. The Red Baron once got lost trying to get to Berlin in spite of bad weather. “I laughed at the clouds and the beastly weather even though the rain came down in buckets. Now and then there was hail. The propeller later looked absurd; beaten by hailstones, it looked like a saw blade. Unfortunately, the weather was so much fun for me that I completely lost track of my position.” (from The Red Baron: The Story of the Fabled Ace in His Own Words.)
In any case, as Libby found out, not flying in rain wasn’t because of any aviation policy of “safety first”; the policy was "win the war first, so we can have leisure to worry about safety." Libby was trained for 30 minutes on how to use a machine gun, then he was shown how to use the gun in the airplane, then sent up in the airplane to try it. The instructor forgot to tell him how to change out the ammunition, and he almost hit the propeller, and the pilot, with the ammunition drum. But he also hit his target with his bullets, commenting that it is hard to miss with forty-seven rounds. After this training, he was qualified to be an observer.
That afternoon (yes, we are still talking about the same day) he went up for his first combat flight. An enemy aircraft attacked and, missing his first opportunity to shoot, Libby shot at even closer range with his forty-seven rounds that he didn’t think required any special aim. And maybe it didn't, to someone who grew up on a ranch, riding and roping. But the German went down in flames and everyone else was greatly impressed with Libby getting his first victory on his first day. Usually, just surviving one’s first combat was a good start.
So Libby's aviation career started off rather well, and that start may have helped him see aviation as better than the trenches. But as an observer (he later became a pilot, and scored many more victories) Libby was flying without a seatbelt, and often even standing up in the cockpit. That's how many observers came to fall out of the airplane (though there were stories of a few who were able to get back in, and in the case of Captain Hedley, a superior officer even saw the event to confirm it.) In Libby’s aircraft, the F.E.2b, the observer's cockpit was even worse; he was in front of the pilot, the engine, and the propeller, and to fire at an enemy coming up behind he had to stand on the airplane itself, facing backwards with just the gun to hang onto.
That rain in France must have been really intolerable to a Colorado boy. Read more in Libby's autobiography Horses Don't Fly.