Flight 3630 was an ordinary Aeroflot journey, running from Mineralnye Vody in the northern Caucasus up to Vilnius, the capital of the Lithuanian SSR, with a stop at Rostov-on-Don. After a brief pause on the ground, the Tu-124 lifted off from Rostov at 2:55 in the afternoon and settled into cruise. By 3:14 it reported passing over Donetsk at 8,400 meters. Controllers asked for a quick climb to 9,000 meters to clear other traffic, and the crew complied without trouble. At 3:31 they radioed in again, unhurried, noting a ground speed of 852 kilometers per hour and estimating they would reach Kremenchuk ten minutes later. Everything about the flight, to that moment, was thoroughly unremarkable, the kind of leg thousands of Soviet passengers flew every week without a second thought.

Then came the fractured transmission at 3:37, the aircraft's registration numbers cried out with that frantic inflection on the last word, and after it, nothing. The plane entered a steep dive as it rolled to the left and slammed into the ground at roughly 950 kilometers per hour, gouging a deep cone-shaped crater and destroying most of the airframe. There had been no distress call describing a problem, no time to work through a checklist, only that one terrible burst of numbers. Whatever seized the aircraft in those final seconds came fast enough that the crew could do little more than key the microphone. Thirty-two passengers and five crew members died on a calm afternoon, in weather so untroubled it was ruled out as a cause before the investigation had properly begun.

Investigators faced a puzzle with most of its pieces missing. The flight data recorder was destroyed beyond any hope of reading it. From the wreckage they could tell that the engines had been at idle, the flaps, spoilers, and landing gear all retracted, and, strangely, that the rudder trim sat fully to the right while the left aileron trim was full up, a combination that would have made the aircraft violently hard to control at speed. They chased every theory. A midair collision with a military drone or a weather balloon left no evidence. There was no sign of structural failure. Fire had scorched parts of the aircraft, but the victims had inhaled no smoke, so the flames were judged to have come after impact, not before. In the end the commission understood what the trim settings would have done, but never how the chain of events began. Flight 3630 remains, quietly, unsolved.