Yes, there are decades of pilots reporting oddball lights in the sky spooking them, and even a New York Times best-seller entitled: "UFOs: Generals, Pilots, and Government Officials Go on the Record." But there has never been a corroborated report of a truly exotic vehicle of obvious extraterrestrial construction (something more than a blob, a Frisbee-looking thing, or other primitive geometric shape) ever being seen in broad daylight and up close.
This is ironic when considering the oddball case of the lawn chair UFO. On July 2nd, 1982, truck driver Larry Walters tied 42 helium-filled balloons to a lawn chair in the backyard of his girlfriend's house in San Pedro, Calif. He shot up to 16,000 feet where a TWA pilot incredulously reported the details of seeing a man adrift like the character in the 2009 cartoon "Up."
An interstellar spaceship zooming through the clouds should make a much bigger impression on pilots. But this has never happened despite thousands of UFO reports per year.
UFOs are almost exclusively seen as just weird lights. And, often the misinterpretation is made that the lights are attached to a physical body, as in the case of the legendary Phoenix lights sighting in 1997 (which Morella references as an outstanding UFO mystery). The Phoenix lights have been debunked as a hoax where flares were attached to a series of helium balloons. Witnesses' imaginations filled in the nonexistent details to describe a monstrous flying delta-shaped vehicle.