​​Faulty Warning System

On January 13, 1977, an Aeroflot Tu-104A was operating a flight from Khabarovsk via Novosibirsk to Alma-Ata. On board were 90 people - 82 passengers and 8 crew members.

The aircraft was approaching its final destination, Alma-Ata. At a distance of 12 kilometers from the airport, while descending through 500 meters and with flaps extended, the left engine’s power began to slowly decrease. Twenty-two seconds later, vibrations appeared. Noticing irregularities in the left engine, the crew retracted the flaps to 20°. Eight kilometers from the airport, the pilots reported a failure of the left engine and their intention to land using the right one. They shut down the left engine and increased power on the right. Two kilometers later, the aircraft, 400 meters to the right of the approach path, began quickly moving back toward the centerline. After another 1,200 meters, it crossed the course line and continued to drift.

At 3.5 kilometers from the runway, at an altitude of 195 meters, the plane abruptly pitched up and climbed to 285 meters. This sudden maneuver caused a sharp loss of speed, and the aircraft entered a stall. During the final radio transmission, the crew uttered two unintelligible words. Three seconds later, at a speed of 150–190 km/h and a pitch angle of 28°, the aircraft slammed into a snow-covered field. The impact tore off the tail. The nose and both wings buried themselves two meters into the ground, exploded, and burned completely. The aircraft crashed 3,280 meters from the runway threshold. Everyone on board died.

The investigation determined that the cause of the crash was a fire in the left engine. Witnesses on the ground saw flames, but the pilots had no indication of it and never activated the fire extinguishing system - the fire warning never triggered. It was found that the fire originated in the area of the left engine due to a fuel leak caused by the destruction of a fuel line section between the booster pump and the fire shutoff valve. The damage likely resulted from heat exposure from a cabin pressurization duct that either ruptured or lost its seal.

As the aircraft slowed during the final approach, the fire intensified, affecting the plane’s controllability. People may have begun suffocating from carbon monoxide and, possibly in panic, rushed toward the tail, shifting the center of gravity rearward. The toxic gas was released by insulation materials that had been heated from the outside of the fuselage. Why the aircraft suddenly pitched up right before the crash - a maneuver that led to the stall - remains unclear, as the flight data recorder stopped working 20 seconds before impact.