One will find, among the most interesting reports of unidentified flying objects collected over the years, that a number do involve observations made by pilots. Such was the case, in fact, with Kenneth Arnold's famous sighting in the summer of 1947, recognized by many as the event which singlehandedly kicked off the era of "flying saucers".
Granted, many would dispute whether pilots are necessarily any better at making trained observations of anomalous aerial phenomenon. "People often think pilots and police officers are trained observers in these regards, but experience has repeatedly shown that they are not," wrote the editors of Skeptical Inquirer in the magazine's January/February 2009 edition. Indeed, a pilot, while skilled at navigating the skies, may not possess a broad knowledge of astronomy, physics, sociology, or even UFO-related literature that might assist them with interpreting their observations in a scientific way.
On the other hand, while pilots do report UFOs, not all of the unidentified craft in question resemble saucers or spaceships of any kind. In my book The Ghost Rockets, I detailed a number of reports over the years of what appear to have been rocket or missile-like objects, which are occasionally reported by pilots even in modern times (although as a historical note, I borrow the term ghost rocket from the name given to aerial phenomenon that was reported over Scandinavia in the summer of 1946).
The book was actually inspired by an exchange I had been having with a friend of mine a while back, who worked with the US space program. I was interested in seeing if there might be records anywhere that dealt with observations of drones or other small aircraft seen flying close to commercial aircraft, and he pointed me in the direction of NASA's Aviation Safety Reporting System (ASRS), a database which collects anonymous reports from pilots, aviation professionals, and even passengers that wish to report hazardous circumstances and other safety issues pertaining to commercial aircraft.
I did manage to find a number of reports in the ASRS that matched my queries for rocket or missile-like objects. Additionally, there were other incidents that, while not matching my criteria for reports of "ghost rockets", nonetheless seemed to describe some fairly unusual aircraft.
One such report involved an incident that occurred in 2010, where a flight instructor had encountered an unusual aircraft during a training flight near Anoka County-Blaine Airport (ANE), outside of Minneapolis, Minnesota. The pilot and students were in contact with Air Traffic Control operators at ANE, and had been cleared for landing at Runway 9. According to the ASRS report, the pilot noted that "Other aircraft were on the frequency but no other aircraft were in our area."
At around this time, the pilot notes that an aircraft was observed to the north, and at a lower altitude. "I considered them 'no factor'," the pilot wrote in the report, "but asked the Tower if they had that aircraft and they replied no."
Within a few moments, one of the students in the left seat of the aircraft observed the object out his window just below the training flight. "It appeared to be the same aircraft we had identified just a couple minutes earlier," the pilot's report reads. "He was heading slightly southeastward. They were pushing us off our final approach to Runway 9. As we corrected to the southeast to avoid this aircraft I told Tower we had an aircraft out our left window within probably 200 [feet]. He did not have him on a transponder and was able to visually see him with field glasses out the Tower window."
At this time, the operators at ANE Tower "tried several times to call this aircraft with no joy." The object, which the pilot's report refers explicitly as an aircraft, was moving more slowly than their plane had been in its approach to ANE. The unidentified aircraft "then proceeded southeast bound conflicting with an aircraft on right down wind for Runway 9. When this event happened we were 2 to 2.5 miles from Runway 9 threshold within Class D airspace. No further event occurred."
In many of the ASRS reports of this sort, no further description or details are given as to the features of such unidentified aircraft. However, within the final sentence of the pilot's report, a rather novel description of the "aircraft" does finally appear:
This unidentified aircraft appeared to be a homebuilt (ultralight?) with an enclosed cabin that looked as if it seated two. It looked similar to a flying egg.
It is interesting that this description did not indicate that the aircraft as a plane, per se, and makes no mention of wings, tail, or other common features, all the while comparing the aircraft to "a flying egg." Given this description, the craft appears to be somewhat reminiscent of the description of an aircraft given by New Mexico State Police officer Lonnie Zamora in April, 1964 near Socorro, NM (this famous UFO sighting is believed by some to have involved a lunar landing module test). Zamora reported coming upon an egg-shaped aircraft which had apparently landed in an arroyo, and observed two individuals in white uniforms outside the craft shortly before it lifted off the ground; as the object took flight, it produced flames and a loud roaring noise that frightened Zamora, because he had been concerned that it "might explode."
It should be noted that the incident report on this "flying egg" refers to the object as having been "an apparently home built aircraft" of some variety. It's not hard to imagine that there may indeed be individuals out there producing such unusual aircraft designs, which may turn up from time to time. This may be the case regardless of whether the builders are hobbyists, independently funded aviation outfits, or the results of other kinds of projects that one might imagine.
As far as the ASRS database reports that fall on the "strange" side of things may go, this one certainly qualifies as being a legitimate -- if somewhat novel -- report of an unusual (and unidentified) flying object.