In 1976 this coastline was a highway in the sky. Soviet holidaymakers streamed toward the sanatoria and beaches of the Black Sea, and Aeroflot fed them south along fixed corridors marked by radio beacons with names like Novodmitrievskaya and Gelendzhik. The Yakovlev Yak-40, a stubby three-engined regional jet, reported passing its checkpoints and holding 5,700 meters. The Antonov An-24, a high-winged turboprop workhorse of the Soviet fleet, reported the same altitude on a route that would cross the first. Both crews did what crews do: they trusted the voice on the radio to keep the layers of traffic apart. That trust was the system. When it held, thousands flew home unremarkably. When it slipped, there was very little else to catch the error.

The controller managing the Western section of Krasnodar had been at his post for more than six hours by the time the Yak-40 entered his airspace. The flight plan called for it to descend after Novodmitrievskaya, but he was busy with other aircraft and let it stay high. At Gelendzhik it reported 5,700 meters again; again he cleared it onward and again did not order it down. Minutes earlier he had waved the An-24 through the same section at the same altitude. Neither crew questioned it - the altitude had been sanctioned, and a sanctioned altitude feels safe. Investigators would later fault the crews for a lapse in vigilance, but the primary finding was blunt and human: the rules of separation had been violated on the ground, by one exhausted person losing track of two dots that were quietly converging.

The collision severed the tail from each aircraft, and both broke apart as they fell into the Black Sea. All seventy people aboard were killed - fifty-two on the An-24, eighteen on the Yak-40, among them named men remembered in the record: Captain Mikhail Gutanov and his crew on one flight, Captain Anatoly Ledenev and his on the other, and dozens of passengers whose journeys simply stopped. Searchers located the wreckage of the An-24 and the tail section of the Yak-40 in water 500 to 600 meters deep, far beyond diver range, and recovered most of the An-24's dead from the surface. But the fuselage of the Yak-40 was never found. Somewhere below the summer swells off Anapa, it remains - and with it the passengers who were never brought home. The reconstruction of what happened came almost entirely from the crackle of preserved radio calls, the last words of people who did not know they were near the end.

Anapa is again what it was before that afternoon: a resort town of pale beaches and shallow, child-friendly water, one of the gentlest stretches of the whole Russian Black Sea coast. Vacationers wade out over the sandbars; gulls work the shoreline. There is no monument here at the water's edge to the flights that fell offshore, and most who visit will never know the sea holds a wreck. That absence is its own kind of memorial - a reminder that catastrophe leaves the fewest traces where it happens over open water. To look out from the beach and imagine the sky above it in 1976 is to feel how thin the margin can be between an ordinary flight home and none at all.