To compensate for the left-wing-low tendency, the crew had adopted a common but dangerous workaround: they fed fuel exclusively from the left wing tank, gradually lightening that side to counteract the roll. The strategy worked for thirty-five minutes after takeoff, with the autopilot managing the resulting asymmetry. But as fuel drained unevenly, the aircraft began banking right. The crew, occupied with their pre-landing checklist, did not notice. The bank angle crept past thirty degrees, triggering warning lights on the instrument panel. Neither the captain, forty-six-year-old Viktor Sumarokov, nor first officer Stanislav Revedovich, forty-three, reacted to the visual warnings. A critical detail: the aircraft's audible bank angle alarm had been removed. Without that aural cue cutting through their task focus, the spiral tightened silently.

Captain Sumarokov eventually sensed something wrong. The excessive bank angle pressed him sideways in his seat, and he ordered Revedovich to slow down. It was too late. At 10,600 meters, the Tu-154 entered a steep downward spiral from which recovery was impossible. The aircraft disappeared from radar shortly after a routine radio call at 3:00 a.m. local time, approximately 160 kilometers from Khabarovsk. It missed its estimated arrival time of 3:45. Nearly an hour later, search and rescue operations began, but heavy snow and near-zero visibility grounded the search aircraft before midnight. Flight 3949 had vanished into the mountainous wilderness of Primorsky Krai, and it would take eleven days to find it.

The search became an exercise in frustration and false leads. Radio Moscow reported flaming wreckage spotted 120 kilometers from Khabarovsk; the Ministry of Emergency Situations denied it. Villagers in Koppi claimed to have heard low-flying aircraft. Residents of Grossevichi reported a crash within their village. Paratroopers deployed by the Russian Army found debris that turned out to belong to older, unrelated crashes. Satellite imagery flagged wreckage near Berezovaya that proved to be nothing. Oil slicks in the Sea of Japan and smoke sightings near Sukpai were investigated and dismissed. In desperation, authorities consulted Juna, a famous Russian clairvoyant, who pointed them toward the Samarga River. That lead also turned up empty. Over 14,000 square meters of terrain were scoured before a chance discovery finally revealed the crash site in the remote mountains.

The impact had carved a crater six feet deep and seventy feet wide. The Tu-154 had struck the mountainside at such velocity that almost nothing recognizable remained. The site was strewn with shredded personal belongings and human tissue, the physical evidence of a high-speed, nose-first impact. The flight recorders, recovered the same day the wreckage was found, were badly damaged; their housings crumpled, the tapes inside cut and ruptured. Investigators could decode the stored data only in fragments. More than fifty personnel were dispatched to recover the remains of the ninety-eight people aboard. What they found confirmed the investigators' worst fear: this was a fully preventable disaster, the result of a known defect left unrepaired and a safety system left uninstalled.

Flight 3949 was the fifth air disaster in Russia in a single week, and the second major crash in less than twenty-two months. The investigation by the Interstate Aviation Committee identified five contributing causes: the pre-existing mechanical defect, the fuel imbalance workaround, the missing audible bank alarm, crew inattention, and catastrophic failures in regional air traffic control. The radar serving the Khabarovsk region had been damaged by a recent storm and was not fully operational. Communications between the pilots and ATC were never recorded due to a tape malfunction. The controller on duty was not actively tracking the aircraft. In the aftermath, audible bank angle alarms were ordered reinstalled on all Tu-154 aircraft. The Russian media outlet Kommersant observed that the country's aviation surveillance system was inadequate for an industry that had been growing rapidly since the dissolution of the Soviet Union, a system struggling to manage the chaos that followed the collapse.