He did not scream. That is the first thing that snags on you about the Frederick Valentich tape. A 20-year-old pilot radios Melbourne Flight Service to say a strange aircraft is "orbiting on top of me," that his engine is now "rough-idling," and finally, flatly: "It is not an aircraft." Then comes seventeen seconds of metallic, scraping noise. Then nothing. On the evening of Saturday, 21 October 1978, Valentich and his rented Cessna 182L simply stopped existing as far as the physical record is concerned.

Here is what is documented rather than imagined. Valentich departed Moorabbin Airport bound for King Island on a clear evening over Bass Strait. Between 19:06 and 19:12 he held a conversation with Flight Service officer Steve Robey, the transcript of which survives in the official Department of Transport file. He reported a large aircraft with four bright lights passing above him at high speed, said it was "orbiting" and that it had a shiny metal surface and a green light. He asked Robey to identify any known traffic in the area; there was none. His final transmission was followed by that unexplained noise and the loss of contact. An air, sea, and land search ran until 25 October and recovered nothing.

The hard evidence cuts in more than one direction, which is exactly why this case refuses to close. The Department of Transport's Aircraft Accident Investigation Summary, approved in 1982, concluded the reason for the disappearance "has not been determined" but presumed the outcome fatal. That is an official Australian government document declining to explain a recorded event. Five years later, in 1983, an engine cowl flap washed ashore on Flinders Island, and the Bureau of Air Safety Investigation determined it came from a Cessna 182 within a serial-number range that included Valentich's tail number GE-DSJ. The Royal Australian Navy Research Laboratory was asked whether drift patterns were consistent with the crash zone. They were not inconsistent.

The skeptical reading is sober and worth taking seriously. Investigators noted Valentich was an inexperienced night pilot who had twice before strayed into cloud and once been reported for flying into a restricted zone. The leading conventional theory holds he became spatially disoriented, possibly flew inverted, and saw his own running lights or the lights of a nearby island reflected back at him — the "orbiting" object being his own aircraft's reflection as he banked. Astronomer and skeptic Brian Dunning has pointed out that several bright celestial bodies, including Venus and the stars of Orion, sat low over the horizon in roughly the direction Valentich was facing, which could account for the four steady lights. Disorientation kills pilots routinely, and the metallic scraping could be a microphone keyed against the airframe as the plane spiraled into the water.

And yet. Disorientation does not obviously explain a pilot calmly reporting a four-lit metallic object that paces him, then reports his engine roughening, then states with eerie composure that the thing is not an aircraft. It does not explain why no significant wreckage was ever recovered from a search that knew approximately where to look. It does not explain the residual cluster of independent reports that night of strange lights over Bass Strait logged by other observers. The skeptics have a plausible mechanism; they do not have a body, a slick, or a closed file.

The inversion worth sitting with is this: in the official world, the burden is always on the witness to prove something anomalous happened. But here the witness was a licensed pilot on an open radio channel, his words preserved verbatim in a government transcript, his aircraft confirmed lost. The anomaly is not that someone claimed to see a UFO. The anomaly is that a calm, competent voice described one in real time to air traffic control and then was erased from the world along with two tons of aluminum — and the people whose job it was to explain it wrote, in their own report, that they could not.

What did Frederick Valentich see in the four seconds between "it is not an aircraft" and the scraping sound? The Australian government has had since 1978 to answer, and its own conclusion is the most unsettling line in the whole file: cause undetermined.